Structural basis for control of secondary vessels in the long-finned eel Anguilla reinhardtii
School of Biomedical Sciences, Department of Anatomy and Developmental Biology, University of Queensland, St Lucia, QLD 4067, Australia
* Author for correspondence at present address: University of Copenhagen, Marine Biological Laboratory, Strandpromenaden 5, DK-3000 Helsingør (e-mail: pvskov{at}bi.ku.dk)
Accepted 24 June 2004
![]() |
Summary |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key words: secondary vessel, interarterial anastomoses, immunohistochemistry, control, structure, organisation, long-finned eel, Anguilla reinhardtii
![]() |
Introduction |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The ability of teleost fishes to regulate perfusion of different vascular
beds is well documented, and is believed to be mediated predominantly by
actions of the autonomic nervous system (for reviews, see
Nilsson and Holmgren, 1993;
Morris and Nilsson, 1994
;
Holmgren, 1995
;
Donald, 1997
). The control of
the coeliaco-mesenteric circulation has received considerable interest, and is
under both adrenergic (Axelsson et al.,
1989
,
2000
;
Sverdrup et al., 1994
) and
neuropeptidergic control (Holmgren et al.,
1985
; Jensen et al.,
1991
; Kågström et al.,
1994
,
1996
; Kågström and
Holmgren, 1997
,
1998
;
Domeneghini et al., 2000
). The
control of the systemic vascular smooth muscle has received little attention
in terms of the possible involvement of non-adrenergic non-cholinergic (NANC)
transmitters.
The involvement of both neural and humoral aminergic transmitters in the
control of the primary systemic vasculature is well documented
(Wahlqvist, 1980; Wahlqvist
and Nilsson 1980
,
1981
), while information on
the control of the secondary vascular system is very limited. Speculation
regarding the regulatory capacity of the secondary vascular system has arisen
not only due to difficulties in obtaining high quality vascular casts, but
more so in relation the physiological significance of this vessel system.
Secondary vessels are currently believed to be under adrenergic control at
least, partly because the administration of smooth muscle relaxants appears to
have some positive impact on the degree of filling by vascular casting agents
(Vogel, 1985a
). This was
supported by the findings of Chopin and Bennett
(1996
), who observed
tyrosine-hydroxylase immunoreactivity in the vicinity of secondary vessels,
which led them to suggest that adrenergic nerves contribute in the regulation
of vascular tone in this vascular system.
The aim of the present study was, via conventional histological procedures and transmission electron microscopy (TEM), to visualise the structure of the vascular wall of primary and secondary vessels of the systemic circulation. A particular goal was to evaluate the degree of association of smooth muscle cells with interarterial anastomoses and secondary vessels, in order to assess the structural capacity for this vascular system to regulate flow. The possible involvement of a suite of NANC components in the control of this vascular system was also investigated immunohistochemically.
![]() |
Materials and methods |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Animals were anaesthetised, heparinised and cannulated as described
previously (Skov and Bennett,
2004), except that no adrenergic blocker was administered. In
brief, the ventral aorta was cannulated via the atrium, and the
animal perfused with 300-1000 ml cold (4°C) heparinised (20 IU
ml-1) saline (0.9% NaCl) until the effluent was clear of any red
blood cells, and subsequently perfusion-fixed with 300-500 ml cold, freshly
prepared, 2% paraformaldehyde (PFA). For histological and immunohistochemical
examination, cutaneous collecting vessels, skin tissue and segmental arteries
and veins with a minimum of surrounding tissue, were dissected free and
postfixed in 4% PFA at 4°C overnight. The following day tissues were
rinsed in three 30 min changes of cold 0.1 mol l-1
phosphate-buffered saline (PBS 0.9% NaCl, pH 7.2).
Scanning electron microscopy
A number of segmental arteries were carefully dissected free of surrounding
tissues for scanning electron microscopy (SEM). Using iris scissors, the
vessels were opened along their longitudinal axis, and pinned flat to a piece
of balsa wood with the luminal side outwards. Vessels were dehydrated in a
series of ethanol (70%, 95% and 3x100% for 1 h each) and critical-point
dried by displacement of absolute alcohol with liquid carbon dioxide. Blood
vessels were mounted on stubs using double-sided carbon tape, platinum coated
and examined by scanning electron microscopy (Jeol 6400, Tokyo, Japan).
Pictures were captured digitally at a resolution of 1024x768 pixels.
Transmission electron microscopy
For TEM, tissues containing segmental arteries or lateral collecting
vessels (LCV) were fixed overnight in a solution of 2.5% glutaraldehyde and 4%
PFA in 0.067 mol l-1 cacodylate buffer at 4°C, washed overnight
in 0.1 mol l-1 sodium cacodylate (pH 7.2). Tissues were then
post-fixed in 1:4 (v:v) 4% osmic acid and 0.1 mol l-1 sodium
cacodylate, washed in several changes of distilled water and stained with 2%
uranyl acetate for 30 min, and washed again. Tissues were then dehydrated in a
graded series of ethanol (50, 70, 90, 95 and 100% for 10 min each, and then 1
h in 100%), cleared in 3 changes of propylene oxide (10 and 2x20 min),
infiltrated in a 1:1 (v:w) mix of propylene oxide and Epon/Araldite mixture,
containing 4 g Epon 812, 2 g Araldite, 4.2 g dodecenyl succinic anhydride
(DDSA), 2.5 g nadic methyl anhydride (NMA) and 0.2 g benzyldimethylamine
(BDMA) overnight, and then in two changes of 100% Epon/Araldite for 7 h each.
Tissues were positioned in embedding trays, covered in Epon/Araldite and
placed under vacuum at -30 mmHg for 1 h (Labec vacuum chamber, Laboratory
Equipment Pty Ltd., Sidney, Australia), and then allowed to polymerise at
60°C for 24 h. Any irrelevant tissue was trimmed away from the block,
which was then sectioned at 100 nm on an Ultracut E microtome (Reichert-Jung,
Vienna, Austria), mounted on copper grids and stained with Reynolds lead
citrate for 2 min using an LKB Ultrastain (LKB, Bromma, Sweden). Sections were
examined using a transmission electron microscope (Jeol 1010, Japan), and
images were captured digitally.
Histology
For histological examinations, tissues were dehydrated in a graded series
of ethanol (70% for 2 h, 2x100% for 2 h and one change of 100% ethanol
overnight). Cutaneous tissues were decalcified at room temperature (RT) for
30-60 min, in a 1:1 solution of 20% (w:v) sodium citrate and 45% formic acid
(v:v) in distilled water, to reduce fractures in the section caused by cutting
mineralised scales. Specimens with large amounts of adipose tissue (skin and
cutaneous collecting vessels) were defatted in Carnoy's fixative (60% ethanol,
30% chloroform and 10% glacial acetic acid) for 2-3 h at RT prior to
dehydration. All tissues were infiltrated in three overnight changes of glycol
methacrylate (Technovit 7100 embedding kit, Heraeus Kulzer GmbH, Wehrheim,
Germany) solution I (Technovit 7100 base with 1 g hardener I per 100 ml),
before being embedded in solution II (solution I plus 1 ml hardener II per 15
ml), all at 4°C.
Tissue blocks were sectioned to water at a thickness of 2-4 µm, collected on plain microscope slides, and dried at 60°C overnight. Sections were stained for 5 min in 1% Lissamine Fast Red in 1% acetic acid at RT, rinsed in water and differentiated for 3-5 min in 1% aqueous phosphomolybdic acid at 56°C, rinsed again and counterstained with 1.5% tartrazine in 1.5% acetic acid for 5 min at RT. Other sections were stained in Toluidine Blue for 1 min, and rinsed in running tapwater. Slides were air-dried overnight at RT, coverslips placed on top using DePeX as mounting medium, viewed and photographed on an Axiophot microscope (Zeiss, Oberkochen, Germany) using a Spot Insight colour camera (3.2.0. Diagnostic Instruments, Inc., Sterling Heights, MI, USA). Images were captured digitally using associated software (Spot v. 3.4.2. for MacOSX) at a 1600x1200 pixels resolution.
Immunohistochemistry
For immunohistochemistry tissues were embedded in glycol methacrylate
(Technovit 8100 embedding kit; Heraeus Kulzer GmbH). Tissues were postfixed in
Carnoy's fixative at 4°C for 2 h before being dehydrated in a series of
ethanol (70% 2 h and 3x100% for 2 h each). Following dehydration,
tissues were infiltrated with three overnight changes of solution I (Technovit
8100 base plus 0.6 g hardener I per 100 ml) at 4°C. Upon transfer to the
last T-8100 solution, tissues were placed under vacuum (-30 mmHg) at RT for
1-2 h, depending on the size of the tissues. This removed any trapped air from
within the tissues, ensuring thorough infiltration. Tissues were kept at
4°C overnight, before being embedded in plastic troughs with solution II
(solution I plus 1 ml hardener II per 30 ml) and covered with acetate film.
Blocks were allowed to polymerise overnight at 4°C, before being bonded
onto histoblocks with Technovit 3040 (Heraeus Kulzer GmbH). Blocks were
sectioned to water using a LKB 2218 Historange microtome (LKB) in 8 µm
thick sections. Test sections were collected on plain slides, dried at
60°C until section had bonded, stained with Toluidine Blue for 1 min,
washed in running tapwater, and dried again at 60°C. Sections were viewed
using a microscope at 20-40x magnification (Zeiss BH-2) to verify that
sections were properly cut and that the desired vessels were found within. If
this was the case, ten consecutive sections were collected on SuperFrost Plus
slides (Menzel-Gläser, Braunschweig, Germany), drained vertically and
air-dried overnight at RT, and sections bordered with wax using a PAP pen
(Dako, Glostrup, Denmark). After every tenth section, a test section was cut
to verify that desired vessels were still found within the block. Slides that
were not immediately processed were stored at 4°C.
Antigen retrieval was performed by treatment with 0.1% trypsin in Tris-buffered saline (TBS) for 30 min at RT. This reaction was stopped by washing in running distilled water for 5-10 min. Endogenous peroxidase was quenched by treating with freshly prepared 0.6% H2O2 in distilled water for 15 min at RT, before being washed in 3x 3 min changes of TBS. Sections were then incubated with 2% BSA (w:v) in TBS containing 0.3% Triton X-100 for 30 min at RT, flicked dry and incubated with primary antibodies overnight at RT (Table 1). Slides were washed for 3x 3 min in TBS, before being incubated with biotinylated goat anti-rabbit or goat anti-mouse IgG (Zymed, San Francisco, CA, USA) for 30-45 min at RT. After another three washes in TBS, sections were incubated with TRITC-conjugated streptavidin (Zymed) for 30 min at RT, washed in three changes of TBS, and mounted in carbonate-buffered glycerol (1 part 0.5 mol l-1 NaHCO3, pH 8.4: 1 part glycerol). Rat colon, intestine or brain was used as positive controls for the antibodies, while substitution of primary antibodies with TBS served as negative controls. Fluorescence images were collected digitally using a confocal fluorescence microscope (Bio-Rad MRC 1024, Philadelphia, PA, USA).
|
![]() |
Results |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Histology
Histological sections of segmental arteries typically contained multiple
origins of interarterial anastomoses within the same section. Each anastomosis
originated as a depression through the endothelial and medial layer of the
wall of the originating artery (Fig.
2). Within the adventitial layer of the vessel an extensive
coiling of the anastomosis was apparent. The anastomosis consequently
straightened and ran transversely along the exterior border of the adventitial
layer, until it reached a secondary vessel running in parallel with the
primary vessel, with which it re-anastomosed. Smooth muscle cells were
associated with the opening of the anastomosis, with the most proximal part
being continuous with the smooth muscle layer of the primary artery from which
it originated (Fig. 2). In the
most proximal part of the segmental artery, secondary vessels were observed as
narrow-bore vessels running within the adventitia and, as secondary vessels
re-anastomosed with each other, large bore vessels lying within a layer of
adipose tissue, entirely outside the adventitia of the corresponding primary
artery. There was commonly more than one secondary artery associated with a
primary vessel. These were occasionally seen to join together
(Fig. 3A-D), or divide to form
several smaller vessels. Near the surface of the fish, wherever a segmental
artery bifurcated, there was a corresponding bifurcation of the associated
secondary vessel. After this bifurcation, secondary vessels gradually became
spatially removed from the segmental artery, although interarterial
anastomoses continued to arise from the primary vessel. These interarterial
anastomoses re-anastomosed and periodically sent projections to the secondary
vessel. Superficially, below the skin, secondary vessels ran parallel to the
exterior surface of the animal.
|
|
The skin of A. reinhardtii was similar to that of other teleost species, with the dermis comprising a compact layer of dense connective tissue and a spongy layer of loose connective and adipose tissue. The epidermis consisted of a basal layer of germinative cells, covered by goblet and mucous cells and a final layer of covering cells. A dense layer of pigment cells covered the basal side of the compact layer. The compact layer itself was poorly vascularised, but large primary blood vessels could occasionally be seen within. Secondary vessels frequently penetrated the compact layer, traversing the width of the layer between bundles of collagen fibres, to exit between the scales of the spongy layer. The scales of A. reinhardtii sit within the spongy layer, and are covered by a dense network of blood vessels, that form a mesh running across the surface of the scales, with occasional hairpin loops projecting up between mucus cells in the vicinity of chloride cells. This vessel system drains via numerous collecting veins into the lateral collecting vessels (LCV), which lie in the compact layer of the dermis. The LCV ran within a tube of dense connective tissue made up from two opposed crescent-shaped structures. The gaps between these, as seen in cross-sections, faced dorsally and ventrally.
Transmission electron microscopy
The LCV was made up of a thick endothelial cell layer on an elastic lamina,
surrounded by an adventitia composed of elastic fibres and loose connective
tissues (Fig. 4A), and was
completely free of smooth muscle cells
(Fig. 4B).
|
One or two layers of smooth muscle cells surrounded the primary segmental arteries. The interarterial anastomoses in the adventitial layer, which was otherwise devoid of smooth muscle, were typically associated with a single smooth muscle cell (Fig. 5A), while secondary vessels were surrounded by a single layer of smooth muscle cells (Fig. 5B). Microvillous projections could be seen within the coils of the interarterial anastomoses, demonstrating that they are not restricted to the opening of the interarterial anastomoses or the wall of the originating primary segmental vessel. Segmental arteries, interarterial anastomoses and secondary vessels were all lined with a continuous basement membrane. Endothelial cells all possessed tight junctions. Structures that appeared to be secretory granules could be seen frequently within the wall of interarterial anastomoses.
|
Immunohistochemistry
Some substance P-like immunoreactivity (SP-like IR) was observed in the
adventitial layer of primary segmental arteries, while both interarterial
anastomoses and secondary vessels stained quite heavily. Similarly, 5-HT-like
IR was observed around segmental arteries, as well as interarterial
anastomoses and secondary vessels (Fig.
6). No IR against any of the antibodies used was observed on
segmental veins (Table 2). In
addition, no calcitonin gene-related peptide (CGRP) or neuropeptide Y
(NPY)-like IR was observed for segmental arteries, interarterial anastomoses
or secondary vessels, but CGRP-like IR fibres were observed in association
with blood vessels between the epidermis and dermis, above the scales. No IR
was observed for SP, 5-HT or NPY in the subepithelial vessels.
|
|
![]() |
Discussion |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The presence of specialised endothelial cells bearing numerous microvilli
has previously been described in the giant gourami Osphronemus gorami
(Vogel and Claviez, 1981). In
the present study, interarterial anastomoses were so dense that these
microvilli completely covered the vessel wall, and were also found within the
interarterial anastomoses. The physiological significance of these microvilli
has not been unequivocally established, but several proposals have been made.
Vogel and Claviez (1981
)
suggested that the microvilli on the luminal surface of the primary artery
might be involved in plasma skimming; a suggestion supported by the in
vivo observation on the glass catfish Kryptopterus bichirrhis
(Steffensen et al., 1986
).
Vogel and Claviez (1981
) also
suggested that these microvilli were involved in the selective recruitment of
leucocytes into the secondary vascular system (SVS), presumably by specialised
adhesion molecules. Lahnsteiner et al.
(1990
) observed that
leucocytes appeared to adhere to the microvilli within the segmental artery,
and this possible function would explain the presence of microvillous
endothelial cells within the iaas.
The organisation of the wall of the primary artery is similar to that of
other vertebrates, with an obvious division into a tunica intima, media and
adventitia, although the medial layer in A. reinhardtii is less well
developed than in terrestrial vertebrates. This appears to be a common trait
for teleosts, and it has been suggested that because fishes live in a fluid
medium of a density similar to that of the body, they have a lower blood
pressure than terrestrial vertebrates, thus the degree of muscularity required
to maintain or regulate vascular tone is not as great (Satchell,
1991,
1992
). Light and transmission
electron microscopy showed that smooth muscle cells were associated with all
interarterial anastomoses, and that the secondary vessels themselves are
surrounded by a layer of smooth muscle, similar to vessels of the primary
circulation. This is not in agreement with the findings of Lahnsteiner et al.
(1990
), who reported that
secondary vessels in Salaria pavo and Zosterisessor
ophiocephalus lack smooth muscle cells, and demonstrated that both these
components of the secondary vascular system in A. reinhardtii possess
the structural requirements for regulating flow. This discrepancy in
observations may be the result of differences in morphology of the secondary
vascular system between the species in question. Secondary vessels are most
commonly thought to give rise to capillary beds at the surface of the animal
(Vogel, 1981
;
Steffensen et al., 1986
;
present study) but in some species it has been reported that they do not
(Lahnsteiner et al., 1990
;
Chopin and Bennett, 1996
). The
finding by Lahnsteiner et al.
(1990
) that secondary vessels
lack a basal membrane is also in contrast to our observations, where a
continuous basement membrane could be clearly distinguished in transmission
electron micrographs of secondary vessels
(Fig. 5B).
In theory, there are a number of possible sites for regulation of flow to
the secondary vascular system; the interarterial anastomoses, secondary
vessels, secondary capillaries or arterioles associated with these, or even
secondary venous vessels. An immediate question that arises from viewing the
histological sections is - to what extent is flow to the secondary vessels
correlated with vascular tone in the corresponding primary artery? As
interarterial anastomoses are an integrated part of the vessel from which they
originate, both in terms of sharing smooth muscle cells, and also with respect
to their physical position within the vessel wall, it seems unlikely that
constriction of the segmental artery can occur without a significant reduction
in the luminal dimensions of the interarterial anastomoses (see
Fig. 2). In contrast, an
increased flow through segmental vessels may not necessarily be accompanied by
an increase in flow through secondary vessels, if they are able to regulate
their luminal diameter independent of primary vascular tone. The regulation of
arterial flow by changes in venous tone was, for a long time, not considered
to play a significant role in teleost physiology, considering the minute
amount of smooth muscle and lack of innervation of venous vessels
(Satchell, 1992). Despite
this, Conklin and Olson (1994
)
demonstrated that the duct of Cuvier, the cardinal vein and the intestinal
vein from Oncorhynchus mykiss were highly responsive to vasoactive
substances, in a dose-dependant manner. Thus, flow and perfusion pressure
through the arterial system may be affected by a change in venous tone. To
what extent this applies to the secondary vascular system was not considered
in this study, but the histological observations and TEM of the LCV do not
lend support to the idea that any regulation occurs at this level. Although
secondary vessels empty into the caudal vein and the duct of Cuvier, any
estimate on the effect of contraction of these vessels on the flow through
secondary vessels would be speculative at best.
Immunoreactivity against SP and 5-HT observed around primary arteries,
interarterial anastomoses and secondary vessels provide direct evidence for
the presence of NANC neural transmitters in the control of blood flow through
arteries of both the primary and secondary vascular system in A.
reinhardtii. To our knowledge the presence of SP or 5-HT-like
immunoreactivity has not previously been demonstrated for systemic blood
vessels in teleosts, although the vascular effects of 5-HT have been widely
investigated in a number of species. It appears that 5-HT induces
vasoconstriction of the branchial respiratory pathway, while it has a dilatory
effect on the systemic vasculature. Vasoconstriction of the branchial
vasculature is mediated by either 5-HT1 or 5-HT2
receptors, since its effects can be abolished by the administration of
methysergide, a general 5-HT1 and 5-HT2 receptor
antagonist (Fritsche et al.,
1992; Sundin et al.,
1995
,
1998
;
Janvier et al., 1996
;
Sundin and Nilsson, 2000
).
Sundin et al. (1998
) showed
that branchial vasoconstriction is completely abolished by LY53857, a specific
5-HT2 antagonist, indicating that this is the sole 5-HT receptor in
this vascular bed. However, the receptors and signaling pathways in the
vasodilatation of the systemic vasculature is less clear. In the coronary
circulation of O. mykiss, 5-HT produces a dose-dependant
vasodilatation, an effect that could be abolished by the addition of
L-NA (N
-nitro-L-arginine), a
nitric oxide synthase (NOS) inhibitor
(Mustafa et al., 1997
). In
contrast, Farrell and Johnson
(1995
) reported that although
5-HT induced vasodilatation in isolated coronary ring preparations from O.
mykiss, this effect was endothelium independent. In addition, a number of
studies have addressed the physiological effects of 5-HT in vivo. The
application of methysergide does not abolish the observed drop in systemic
resistance, demonstrating that other 5-HT receptor subtypes mediate this
vasodilatation. Janvier et al.
(1996
) showed that a 5-HT
mediated drop in systemic resistance in A. anguilla could not be
abolished by the administration of antagonists for any of the four known
mammalian 5-HT receptor subtypes. Similar results have been obtained from
G. morhua (L. Sundin, personal communication). Thus it appears that
teleosts posses a suite of 5-HT receptor subtypes mediating vasodilatation,
which are sufficiently different from their mammalian equivalents not to
respond to mammalian antagonists (S. Holmgren, personal communication).
The available data on the effects of SP on the teleostean vasculature are
limited, and somewhat contradictory. In mammals SP has been shown to decrease
vascular resistance in numerous vascular beds
(Dockray, 1994). In the
gastrointestinal system of the Atlantic cod, mammalian SP has a dual effect,
being a potent constrictor of intestinal smooth muscle
(Holmgren et al., 1985
; Jensen
et al., 1987
,
1991
), thereby increasing
gastrointestinal motility, but also a potent vasodilator of intestinal
arteries (Jensen et al.,
1991
). Kågström et al.
(1996
) examined the in
vivo effects in O. mykiss of trout SP (tSP), which has three
amino acid substitutions compared with mammalian SP
(Jensen and Conlon, 1992
), and
found that it caused a significant increase in both systemic and coeliac
resistance. In contrast to the effects of mammalian SP on coronary arteries
(Farrell and Johnson, 1995
),
tSP had no vasodilator effect on relaxed or precontracted small gut arteries
(Kågström and Holmgren,
1998
). Based on this limited data set, it is difficult to
interpret the presence of SP-like immunoreactivity or the signalling pathways
involved in segmental and secondary vessels in A. reinhardtii.
The effects of circulating adrenaline, noradrenaline and isoprenaline on
flow rates through the isolated tail of G. morhua have been well
documented (Wahlqvist, 1980;
Wahlqvist and Nilsson, 1980
,
1981
), as has the neural
component of this system (Wahlqvist and
Nilsson, 1981
). However, immunohistochemistry against tyrosine
hydroxylase, the enzymatic precursor to adrenaline, did not reveal any
adrenergic innervation. This is in contrast to previous findings by Chopin and
Bennett (1996
), which showed
the presence of tyrosine-hydroxylase immunoreactive fibres in the periphery of
secondary vessels in Arius graeffei. This cannot necessarily be
interpreted as the absence of that vasoactive substance, but may merely imply
lack of cross-reactivity of the antibody
(Holmgren, 1995
;
Kågström and Holmgren,
1998
). This could potentially also explain the negative results
for NPY, and stresses the need for a perfusion protocol for secondary vessels
that would allow for an assessment of the potency and effects of various
vasoactive substances.
The presence of CGRP-like IR on capillaries of the secondary vascular
system, implies that regulation of flow through the secondary vascular system
may also occur at this level. The presence of CGRP has been demonstrated by
immunohistochemical methods in a number of systemic, nonvisceral, vascular
beds from numerous species across divergent phyla (mammals, fishes,
amphibians, molluscs etc.). Intradermal injections of CGRP have demonstrated
its effects as a potent vasodilator at the microvascular level in human
(Brain et al., 1985), rabbit
(Brain and Williams, 1985
) and
rat skin (Chu et al., 2001
).
Perfusion studies on the rainbow trout gut have shown that CGRP is a potent
endothelium-independent vasodilator of adrenaline-precontracted gut arteries
from O. mykiss, whose effect is mediated by the CGRP-1 receptor
(Kågström and Holmgren,
1998
).
The findings presented here demonstrate that secondary vessels possess the structural requirements for independent regulation of flow, and are consistent with the hypothesis that a suite of NANC neurotransmitters contribute in the regulation of blood flow through the secondary vascular system. A better knowledge of the control mechanisms of the secondary vascular system would bring us closer to understanding the physiological and physical conditions under which the secondary vascular system may contribute to the overall physiology of actinopterygian fishes.
![]() |
Acknowledgments |
---|
![]() |
References |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Axelsson, M., Thorarensen, H., Nilsson, S. and Farrell, A. P. (2000). Gastrointestinal blood flow in the red Irish lord, Hemilepidotus hemilepidotus: long term effects of feeding and adrenergic control. J. Comp. Physiol. B 170,145 -152.[Medline]
Axelsson, M., Driedzic, W. R., Farrell, A. P. and Nilsson, S. (1989). Regulation of cardiac output and gut blood flow in the sea raven, Hemitripterus americanus. Fish Physiol. Biochem. 6,315 -326.
Brain, S. D. and Williams, T. J. (1985). Inflammatory oedema induced by synergism between calcitonin gene-related peptide (CGRP) and mediators of increased vascular permeability. Br. J. Pharm. 86,855 -860.[Abstract]
Brain, S. D., Williams, T. J., Tippins, J. R., Morris, H. R. and MacIntyre, I. (1985). Calcitonin gene-related peptide is a potent vasodilator. Nature 313, 54-56.[Medline]
Chopin, L. K., Amey, A. P. and Bennett, M. B. (1998). A systemic secondary vessel system is present in the teleost fish Tandanus tandanus and absent in the elasmobranchs Carcharhinus melanopterus and Rhinobatus typus and in the dipnoan Neoceratodus forsteri. J. Zool. Lond. 246,105 -110.
Chopin, L. K. and Bennett, M. B. (1996). Morphology and tyrosine-hydroxylase immunohistochemistry of the systemic secondary vessel system of the blue catfish, Arius graeffei. J. Morphol. 229,347 -356.[CrossRef]
Chu, D. Q., Legon, S., Smith, D. M., Costa, S. K. P., Cuttitta, F. and Brain, S. D. (2001). The calcitonin gene-related peptide (CGRP) antagonist CGRP8-37 blocks vasodilation in inflamed rat skin: involvement of adrenomedullin in addition to CGRP. Neurosci. Lett. 310,169 -172.[CrossRef][Medline]
Conklin, D. J. and Olson, K. R. (1994). Compliance and smooth muscle reactivity of rainbow trout (Oncorhynchus mykiss) vessels in vitro. J. Comp. Physiol. B 163,657 -663.
Dewar, H., Brill, R. W. and Olson, K. R. (1994). Secondary circulation of the vascular heat exchangers in skipjack tuna, Katsuwonus pelamis. J. Exp. Zool. 570,566 -570.
Dockray, G. J. (1994). Substance P and other tachykinins. In Gut Peptides: Biochemistry and Physiology (ed. J. H. Walsh and G. J. Dockray), pp.401 -422. New York: Raven Press Ltd.
Domeneghini, C., Radaelli, G., Arrighi, S., Mascarello, F. and Veggetti, A. (2000). Neurotransmitters and putative neuromodulators in the gut of Anguilla anguilla (L.). Localizations in the enteric nervous and endocrine systems. Eur. J. Histochem. 44,295 -306.[Medline]
Donald, J. A. (1997). Autonomic nervous system. In The Physiology of Fishes (ed. D. H. Evans), pp.407 -439. Boca Raton, New York: CRC Press LCC.
Farrell, A. P. and Johnson, J. A. (1995). Vasoactivity of the coronary artery of rainbow trout, steelhead trout, and dogfish: lack of support for non-prostanoid endothelium derived relaxation factors. Can. J. Zool. 73,1899 -1911.
Fritsche, R., Thomas, S. and Perry, E. (1992).
Effects of serotonin on circulation and respiration in the rainbow trout
Oncorhynchus mykiss. J. Exp. Biol.
173, 59-73.
Holmgren, S. (1995). Neuropeptide control of the cardiovascular system in fish and reptiles. Braz. J. Med. Biol. Res. 28,1207 -1216.[Medline]
Holmgren, S., Grove, D. J. and Nilsson, S. (1985). Substance P acts by releasing 5-hydroxytryptamine from enteric neurons in the stomach of the rainbow trout, Salmo gairdneri. Neurosci. 14,683 -693.[CrossRef][Medline]
Ishimatsu, A., Iwama, G. K. and Heisler, N. (1995). Physiological roles of the secondary circulatory system in fish. In Advances in Comparative and Environmental Physiology, vol. 21 (ed. N. Heisler), pp.215 -236. Berlin: Springer-Verlag.
Janvier, J.-J., Peyraud-Waitzenegger, M. and Soulier, P. (1996). Effects of serotonin on the cardio-circulatory system of the European eel (Anguilla anguilla) in vivo. J. Comp. Physiol. B 166,131 -137.[Medline]
Jensen, J. and Conlon, J. M. (1992). Substance-P-related and neurokinin-A-related peptides from the brain of the cod and trout. Eur. J. Biochem. 206,659 -646.[Abstract]
Jensen, J., Axelsson, M. and Holmgren, S. (1991). Effects of substance P and vasoactive polypeptide on gastrointestinal blood flow in the Atlantic cod, Gadus morhua. J. Exp. Biol. 156,361 -373.
Jensen, J., Holmgren, S. and Jönsson, A. (1987). Substance P-like immunoreactivity and the effects of tachykinins in the intestine of the Atlantic cod, Gadus morhua. J. Autonom. Nerv. Syst. 20, 25-33.[CrossRef][Medline]
Kågström, J. and Holmgren, S. (1997). VIP-induced relaxation of small arteries of the rainbow trout, Oncorhynchus mykiss, involves prostaglandin synthesis but not nitric oxide. J. Autonom. Nerv. Syst. 63, 68-76.[CrossRef][Medline]
Kågström, J. and Holmgren, S. (1998). Calcitonin gene-related peptide (CGRP), but not tachykinins, causes relaxation of small arteries from the rainbow trout gut. Peptides 19,577 -584.[CrossRef][Medline]
Kågström, J., Holmgren, S., Olson, K. R., Conlon, J. M. and Jensen, J. (1996). Vasoactive effects of native tachykinins in the rainbow trout, Oncorhynchus mykiss. Peptides 17,39 -45.[CrossRef][Medline]
Kågström, J., Axelsson, M. and Holmgren, S.
(1994). Cardiovascular responses to scyliorhinin I and II in the
rainbow trout, Oncorhynchus mykiss, in vivo and in vitro.
J. Exp. Biol. 191,155
-166.
Lahnsteiner, F., Lametschwandtner, A. and Patzner, R. A. (1990). The secondary blood vessel system of segmental arteries and dorsal aorta in Blennius pavo and Zosterisessor ophiocephalus. Histology, fine structure and SEM of vascular corrosion casts. Scan. Microsc. 4,111 -124.
Morris, J. L. and Nilsson, S. (1994). The circulatory system. In Comparative Physiology and Evolution of the Autonomic Nervous System, vol. 4 (ed. S. Nilsson and S. Holmgren), pp. 193-246. Singapore: Harwood Academic Publishers.
Mustafa, T., Agnisola, C. and Hansen, J. K. (1997). Evidence for NO-dependent vasodilation in the trout (Oncorhynchus mykiss) coronary system. J. Comp. Physiol. B 167,98 -104.
Nilsson, S. and Holmgren, S. (1993). Autonomic nerve functions. In The Physiology of Fishes (ed. D. H. Evans), pp. 279-313. Boca Raton, New York: CRC Press.
Olson, K. R. (1996). Secondary circulation in fish: anatomical organization and physiological significance. J. Exp. Zool. 275,172 -185.[CrossRef]
Satchell, G. H. (1991). The peripheral circulation. In Physiology and Form of Fish Circulation, pp. 41-57. Cambridge, New York, Melbourne: Cambridge University Press.
Satchell, G. H. (1992). The venous system. In The Cardiovascular System, vol.XIIA (ed. W. S. Hoar, D. J. Randall, and A. P. Farrell), pp. 141-183. New York: Academic Press.
Skov, P. V. and Bennett, M. B. (2004). The secondary vascular system of Actinopterygii: interspecific variation in origins and investment. Zoomorph. 123, 55-64.[CrossRef]
Steffensen, J. F., Lomholt, J. P. and Vogel, W. O. P. (1986). In vivo observations on a specialized microvasculature, the primary and secondary vessels in fishes. Acta Zool. Stockholm 67,193 -200.
Sundin, L. and Nilsson, G. E. (2000). Branchial and circulatory responses to serotonin and rapid ambient water acidification in rainbow trout. J. Exp. Zool. 287,113 -119.[CrossRef][Medline]
Sundin, L., Davison, W., Forster, M. and Axelsson, M.
(1998). A role for 5-HT2 receptors in the gill vasculature of the
Antarctic fish Pagothenia borchgrevinki. J. Exp.
Biol. 201,2129
-2138.
Sundin, L., Nilsson, G. E., Block, M. and Löfman, C. O. (1995). Control of gill filament blood flow by serotonin in the rainbow trout, Oncorhynchus mykiss. Am. J. Physiol. 268,R1224 -R1229.[Medline]
Sverdrup, A., Krüger, P. G. and Helle, K. B. (1994). Role of the endothelium in regulation of vascular functions in two teleosts. Acta Physiol. Scand. 152,419 -433.[Medline]
Vogel, W. O. P. (1981). Struktur und organisationsprinzip im Gefässsystem der Knochenfische. Gegenbaurs morphol. Jahrb., Leipzig 127,772 -784.
Vogel, W. O. P. (1985a). Systemic vascular anastomoses, primary and secondary vessels in fish, and the phylogeny of lymphatics. Alfred Benz. Symp.143 -159.
Vogel, W. O. P. (1985b). The caudal heart of fish: not a lymph heart. Acta Anat. 121, 41-45.[Medline]
Vogel, W. O. P. and Claviez, M. (1981). Vascular specialization in fish, but no evidence for lymphatics. Z. Naturforsch. 36C,490 -492.
Wahlqvist, I. (1980). Effects of catecholamines on isolated systemic and branchial vascular beds of the cod, Gadus morhua. J. Comp. Physiol. B 137,139 -143.
Wahlqvist, I. and Nilsson, S. (1980). Adrenergic control of the cardiovascular system of the Atlantic cod, Gadus morhua, during `stress'. J. Comp. Physiol. B 137,145 -150.
Wahlqvist, I. and Nilsson, S. (1981). Sympathetic nervous control of the vasculature in the tail of the Atlantic cod, Gadus morhua. J. Comp. Physiol. 144,153 -156.