1 Department of Endocrinology M
and Medical Research Laboratories, Physiologically,
growth hormone (GH) is secreted in pulses with episodic bursts shortly
after the onset of sleep and postprandially. Such pulses increase
circulating levels of free fatty acid and glycerol. We tested whether
small GH pulses have detectable effects on intercellular glycerol
concentrations in adipose tissue, and whether there would be regional
differences between femoral and abdominal subcutaneous fat, by
employing microdialysis for 6 h after administration of GH (200 µg)
or saline intravenously. Subcutaneous adipose tissue blood flow (ATBF)
was measured by the local Xenon washout method. Baseline of
interstitial glycerol was higher in adipose tissue than in blood
[220 ± 12 (abdominal) vs. 38 ± 2 (blood) µmol/l,
P < 0.0005; 149 ± 9 (femoral)
vs. 38 ± 2 (blood) µmol/l, P < 0.0005] and higher in abdominal adipose tissue compared with
femoral adipose tissue (P < 0.0005).
Administration of GH induced an increase in interstitial glycerol in
both abdominal and femoral adipose tissue (ANOVA: abdominal,
P = 0.04; femoral, P = 0.03). There was no overall
difference in the response to GH in the two regions during the study
period as a whole (ANOVA: P = 0.5),
but during peak stimulation of lipolysis abdominal adipose tissue was,
in absolute but not in relative terms, stimulated more markedly than
femoral adipose tissue (ANOVA: P = 0.03 from 45 to 225 min). Peak interstitial glycerol values of 253 ± 37 and 336 ± 74 µmol/l were seen after 135 and 165 min in
femoral and abdominal adipose tissue, respectively. ATBF was not
statistically different in the two situations (ANOVA:
P = 0.7). In conclusion, we have shown
that a physiological pulse of GH increases interstitial glycerol
concentrations in both femoral and abdominal adipose tissue, indicating
activated lipolysis. The peak glycerol increments after GH were higher
in abdominal adipose tissue, perhaps due to a higher basal rate of
lipolysis in this region.
abdominal tissue; lipolysis; hormones; pulsatile
secretion; regions
IN NORMAL SUBJECTS, growth hormone (GH) is secreted in
a pulsatile manner with episodic bursts shortly after the onset of sleep and a few hours postprandially. During a 24-h period, ~0.5 mg
is secreted in 8-12 pulses of ~30 min duration; during
spontaneous bursts, serum concentrations of 15-20 µg/l are often
encountered (18). A key metabolic effect of GH is stimulation of
lipolysis in adipose tissue and subsequent release of free fatty acids
(FFA) and glycerol. It has recently been shown that small short-lived physiological pulses of GH induce a dose-dependent stimulation of lipid
oxidation and increase circulating levels of FFA and glycerol (33, 34).
It has also been reported that pulsatile GH exposure increases whole
body palmitate flux (8).
Patients with GH deficiency (GHD) are at increased risk of
atherosclerosis and coronary artery disease (7, 32, 38) and have
increased amounts of abdominal fat, which has been associated with
cardiovascular disease (7, 14); GH treatment has been reported to
specifically reduce the amount of visceral fat in both GHD patients and
normal adults (7, 24) and to reduce abdominal subcutaneous fat mass
selectively in children (39).
The current study was designed to test the hypotheses that small
physiologically meaningful GH pulses have detectable effects on
intercellular glycerol concentrations in adipose tissue and that these
effects may be most prominent in central subcutaneous fat of the
abdomen. To pursue this, we examined two different regions of
subcutaneous adipose tissue, abdominal and femoral, after insertion of
microdialysis fibers thus enabling assessment of regional changes in
glycerol content after exposure to either GH or saline.
Subjects. Eight healthy males gave
their written informed consent after receiving oral and written
information concerning the study according to the Declaration of
Helsinki II. The study was approved by the Aarhus County Ethical
Scientific Committee.
Experimental protocol. Subjects were
admitted to the Clinical Research Center in the morning after an
overnight fast (10-12 h) without any caffeine consumption or
cigarette smoking; only ingestion of tap water was allowed.
Participants were asked not to perform major physical exercise, to
consume a weight-maintaining carbohydrate-rich diet for the last 3 days
before examination, and to refrain from alcohol intake on the day
before investigation. The average age, weight, and body mass index of
the subjects was 25.5 ± 1.3 (23-33) [mean ± SE
(range)] yr, 78.9 ± 2.7 (68-90) kg, and 23.6 ± 0.6 (21.1-26.0) kg/m2,
respectively. Participants were placed in the supine position in a bed
in light clothes at room temperature ~22-24°C and remained there throughout the study. One intravenous catheter (Viggo,
Helsingborg, Sweden) was placed in an antecubital vein for infusion and
another in a vein draining a hand that was warmed in a box with an air temperature ~65°C to provide arterialized blood. Each subjects was studied two times in a randomized manner with at least 2-wk intervals. After 1 h of calibration with perfusion of the microdialysis catheters (see below), either GH (200 µg dissolved in NaCl) or NaCl
was given intravenously over 25 min. Arterialized blood samples were
drawn every 15 min for 7 h starting 60 min before infusion of GH or
NaCl. Indirect calorimetry was performed in the basal period after 45 min of rest and 4 h after infusion of either GH or NaCl. No untoward
clinical events occurred.
Microdialysis and calculations.
Microdialysis fibers (CMA 60 microdialysis catheter; CMA, Stockholm,
Sweden) were placed in abdominal and femoral subcutaneous adipose
tissue after anesthetization of the skin with 0.05 ml lidocaine at the
sites of perforation of the skin. The microdialysis catheters have a
molecular cutoff of 20 kDa. Immediately after placement, perfusion of
the fibers was started at a rate of 2 µl/min with a Ringer-acetate
solution containing glycerol in a concentration of 25 mmol/l. At a
perfusion rate of 2 µl/min, the exchange over the fiber did not reach
100% equilibrium, and subsequently, the internal reference calibration technique was used to calculate the relative recovery (RR; see Refs. 31
and 42). To the perfusate, a small amount of
[3H]glycerol was
added, and in the perfusate and in each dialysate sample the specific
activity of
[3H]glycerol was
measured. The RR was calculated for each dialysate sample as
ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
where
is disintegrations per minute in
the perfusate and
is
disintegration per minute in the dialysate. It is assumed that the RR
of the unlabeled glycerol in the dialysate equals the relative loss of
the labeled glycerol from the perfusate. The mean RR was 39 ± 1%,
and the coefficient of variation (CV) of the RRs determined for each
individual was 10 ± 1%. The overall mean of the RRs for each
individual was used for further calculations.
Interstitial concentration was calculated as
![]() |
Blood flow measurements. In six
subjects, the subcutaneous adipose tissue blood flow (ATBF) in the
abdominal region in which dialysis was performed was measured by the
local 133Xe washout method (27).
In short, 3.7 MBq (0.1 ml) 133Xe
were injected in the subcutaneous area of interest, equivalent to a
whole body radiation dose of 0.5 mSv. Disappearance of
133Xe was monitored with a 2 × 2-in. NaI detector (model 905) connected to a photomultiplier
base (model 276; EG&G Ortec, Wokingham, Berks, UK) covered by a
cylindrical copper collimator and coupled to a multichannel AceMate
(model 925) amplifier (EG&G Ortec). The system was connected to a
computer for simultaneous sampling. Counts were collected
every minute and were plotted on a semilogarithmic diagram as a
function of time. ATBF was calculated as
![]() |
Indirect calorimetry. Indirect calorimetry (Deltatrac Metabolic Monitor; Datex, Helsinki, Finland) with a ventilated hood at 40 l/min was performed; energy expenditure, respiratory quotient, and 24-h excretion of urea were measured from the excretion rate of urea in urine collected during the entire study period, and glucose, protein, and lipid oxidation were calculated (10). Calibration of the system was done by combustion of a known amount of 99.6% ethanol.
Assays. Plasma glucose was measured
immediately after sampling in duplicate on an autoanalyzer (Beckman
Instruments, Palo Alto, CA) by the glucose oxidase method. GH was
measured with a double monoclonal immunofluorometric assay (DELFIA;
Wallac Oy, Turku, Finland). The interassay CV in samples varied between
1.7 and 2.4%, the intra-assay CV varied between 1.9 and 3.0% for GH concentrations of 12.08 and 0.27 µg/l, and the detection limit was
0.01 µg/l. Serum insulin was measured by enzyme-linked immunosorbent assay, employing a two-site immunoassay. The assay does not detect proinsulin, split-(3233)- and des-(31
32)-proinsulin, whereas split-(65
66)- and des-(64
64)-proinsulin cross-react 30 and 63%, respectively (1). The intra-assay CV was 2.0%
(n = 75) at a serum level of 200 pM.
Serum FFA was determined by a colorimetric method employing a
commercial kit (Wako Chemicals, Neuss, Germany). Blood samples for
determination of alanine, glycerol, 3-hydroxybutyrate (3-OHB), and
lactate were deproteinized with perchloric acid and were assayed by an
automated fluorometric method (29). Plasma glucagon was
measured by an RIA (35). Dialysate glycerol was measured by an
automated spectrophotometric kinetic enzymatic analyzer (CMA 600; CMA).
Statistical analysis. All statistical
calculations were done with SPSS for Windows version 8.0 (SPSS,
Chicago, IL). Data were examined by Student's two-tailed unpaired and
paired t-tests. Repeated-measures
ANOVA (GLM) was used to test for differences with time between the GH
situation and the placebo situation, i.e., to examine whether more
glycerol was released in the GH situation compared with the placebo
situation (the interaction between time and treatment), and for
comparison between changes in the femoral and abdominal region based on
values (i.e., GH
control). Results are expressed as means ± SE. Significance levels under 5% were considered significant.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Circulating hormones. In Fig.
1, the pertinent hormones are illustrated.
Administration of GH increased GH to a peak of 17.7 ± 2.2 µg/l
from baseline values of 0.2 ± 0.1 µg/l, whereas in the control
situation serum GH was constant (ANOVA:
P = 0.0005). Serum insulin and
glucagon stayed constant around 20 ± 1 pmol/l and 54 ± 2 ng/l,
respectively, throughout the study during both treatments (ANOVA:
insulin, P = 0.7; glucagon,
P = 0.8), although there was
a time-treatment interaction in the profile of insulin (ANOVA:
P = 0.04).
|
Lipid intermediates in blood. Baseline
values were comparable with regard to all three intermediates
[FFA: 0.44 ± 0.05 (GH) vs. 0.43 ± 0.04 (NaCl) mmol/l;
3-OHB: 74 ± 22 (GH) vs. 95 ± 24 (NaCl) mol/l; glycerol: 34 ± 3 (GH) vs. 42 ± 3 (NaCl) mol/l;
P (all) = not significant; Fig.
2].
|
The administration of GH induced an increase in all three lipid intermediates, with a peak in glycerol of 79 ± 7 mol/l after 135 min, FFA of 0.90 ± 0.08 mmol/l after 165 min, and 3-OHB of 269 ± 90 mol/l after 195 min (ANOVA: FFA, P = 0.0005; 3-OHB, P = 0.0005; glycerol, P = 0.002). In the placebo situation, there was a slight significant increase in FFA with time and no change in glycerol and 3-OHB.
Interstitial glycerol in abdominal and femoral adipose
tissue: GH vs. placebo. Administration of GH induced
changes in interstitial glycerol comparable with the changes observed
in blood (Fig. 3). Baseline values were
higher in adipose tissue than in blood [220 ± 12 (abdominal) vs. 38 ± 2 (blood), P < 0.0005; 149 ± 9 (femoral) vs. 38 ± 2 (blood),
P < 0.0005], whereas baseline
values of interstitial glycerol were comparable in the two treatments
[abdominal adipose tissue: 230 ± 15 (GH) vs. 208 ± 21 (NaCl) µmol/l, P = 0.4; femoral adipose tissue: 148 ± 11 (GH) vs. 151 ± 14 (NaCl) µmol/l,
P = 0.9]. Administration of GH
induced an increase in interstitial glycerol compared with basal levels
in both abdominal and femoral adipose tissue (ANOVA: abdominal,
P = 0.04; femoral,
P = 0.03). There was no effect of
saline administration in interstitial glycerol with time in either
abdominal or femoral adipose tissue (ANOVA: abdominal,
P = 0.7; femoral,
P = 0.3).
|
Interstitial glycerol in abdominal vs. femoral adipose
tissue. The interstitial glycerol level was higher in
abdominal adipose tissue compared with femoral adipose tissue
[220 ± 12 (abdominal) vs. 149 ± 9 (femoral) µmol/l,
P < 0.0005]. There was no
overall difference in the response to GH in the two regions during the study period as a whole (ANOVA: P = 0.5). However, during the period with the most marked increments in
glycerol concentrations in blood and subcutaneous tissue, the absolute
increment was more pronounced in abdominal adipose tissue than the
femoral adipose tissue (ANOVA: P = 0.03, from time = 45-225 min; Fig. 4).
Peak interstitial glycerol values of 253 ± 37 and 336 ± 74 µmol/l were seen after 135 and 165 min in femoral and abdominal
adipose tissue, respectively. However, due to the difference in basal
glycerol values in abdominal and femoral adipose tissue, the relative
increase over basal was similar. At the time of maximal stimulation of lipolysis, there was a 1.5-fold increase in the release of glycerol in
the abdominal adipose tissue (time = 165 min) and a 1.3-fold increase
in release of glycerol in the femoral adipose tissue (time = 135 min;
P = 0.5). Thus, despite greater
absolute increases in interstitial glycerol in abdominal adipose
tissue, the relative increases were similar.
|
Glucose and gluconeogenic intermediates in
blood. Plasma glucose stayed constant throughout the
study during both treatments (ANOVA: P = 0.6; Fig. 5). Alanine and lactate,
however, declined with time during both treatments (ANOVA:
P = 0.0005). Administration of GH
caused an accentuated decline in alanine (ANOVA:
P = 0.0005), whereas lactate did not
differ during the two treatments (ANOVA: P = 0.7; Fig. 5).
|
Abdominal ATBF. ATBF was not
statistically different during the two treatments [2.8 ± 0.6 (saline) vs. 3.8 ± 0.9 (GH) ml · 100 g1 · min
1,
P = 0.2, n = 6] and stayed constant
throughout the study period.
Energy expenditure. Energy expenditure
was constant on the day of saline infusion [1,765 ± 46 (basal) vs. 1,760 ± 50 (infusion) kcal/24 h,
P = 0.9], whereas energy
expenditure increased on the day of GH infusion [1,736 ± 42 (basal) vs. 1,839 ± 47 (infusion) kcal/24 h,
P = 0.01]. There was a
tendency toward a decrease in urinary nitrogen excretion during the day
of GH infusion [12.0 ± 1.0 (GH) vs. 16.1 ± 2.4 (saline)
g/24 h, P = 0.06 (n = 7)]. Basal measurements on
the two study days were comparable (data not shown). The respiratory
quotient decreased in both situations [saline: 0.83 ± 0.01 (basal) vs. 0.82 ± 0.01 (infusion),
P = 0.01; GH: 0.84 ± 0.02 (basal)
vs. 0.80 ± 0.01 (infusion), P = 0.02], with a tendency to a greater decrease during the day of GH
infusion [decrease:
0.02 ± 0.01 (saline) vs.
0.04 ± 0.01 (GH), P = 0.1]. Protein oxidation decreased [399 ± 34 (GH) vs.
534 ± 81 (saline) kcal/24 h, P = 0.06], lipid oxidation increased [1,001 ± 67 (GH) vs.
745 ± 91 (saline) kcal/24 h, P = 0.01], and glucose oxidation was unchanged [439 ± 22 (GH) vs. 464 ± 62 (saline) kcal/24 h, P = 0.7].
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The present study was undertaken to define the effects of GH on regional interstitial glycerol concentrations in abdominal and in femoral fat. Our main findings are that a single GH pulse increases interstitial glycerol concentrations in both femoral and abdominal adipose tissue, the absolute increase being more prominent in the abdomen. It should be noted that, with the present dosage of GH, we obtained a serum profile closely resembling a large spontaneous secretory burst with regard to duration (25 min) and magnitude (17.7 ± 2.2 µg/l; see Ref. 18).
It is well established that GH is a hormone with potent lipolytic and protein-sparing effects, and the impact of a single bolus of GH, imitating a physiological pulse, has been characterized in terms of circulating levels of lipid intermediates (20, 33, 34, 36). Here, by indirect calorimetry, we found an increase in lipid oxidation illustrating the effect of GH on whole body metabolism. We found that glycerol levels in the interstitial fluid of subcutaneous adipose tissue were significantly affected by a physiological pulse of GH in a time-dependent manner closely paralleling the picture seen in blood. The identical patterns of changes in glycerol and FFA in the circulation and glycerol in the interstitial fluid with peak values between 135 and 180 min probably reflect that both substances reach equilibrium fast due to a rapid turnover. The present data fit well with previous observations linking nocturnal peaks of GH with the maximum level of FFA 120 min later (40). At present, the exact mode of the intracellular action of GH is not completely known. In vitro GH possesses both insulin-like and lipolytic actions (13), with the insulin-like action of GH probably being governed by intracellular Ca2+ levels (11). The lipolytic actions may be mediated through stimulation of gene expression after binding of the GH receptor with JAK2 tyrosine kinase and subsequent activation of the complex (2). The intracellular signaling process leading to stimulation of lipolysis is not known in detail but appears to involve activation of adenylyl cyclase stimulating intracellular cAMP production (48), which initiates a chain of reactions, including RNA and protein synthesis, resulting in the activation of hormone-sensitive lipase. In vitro, this activation of lipolysis takes 1-2 h, which is entirely consistent with our in vivo findings.
It is not likely that the elevated glycerol concentrations may have been influenced by changes in circulating levels of insulin or glucagon; in accordance with previous studies (33, 34, 46), we observed virtually unchanged concentrations of the two hormones. Furthermore, because ATBF estimated by Xenon washout did not decrease after administration of GH, it appears by far most plausible that the increased glycerol concentration is a direct consequence of GH stimulation of lipolysis (4, 17, 22). Previously, it has been shown that small amounts of GH do not acutely affect blood flow in the forearm (33, 34), compatible with a lack of any effects on flow in adipose tissue.
Microdialysis allows continuous monitoring of changes of fluxes of a variety of compounds from interstitial fluid to the dialysate, and it has been utilized in a large number of tissues in the human body since it was first introduced (30). True equilibrium is not accomplished across the membrane, unless a very low flow rate is used, and RR of an internal standard may be used to correct the ensuing deficit (31, 42). Thus the changes in estimated interstitial glycerol concentration can be seen as an index of lipolysis (4, 17, 22). Calculated baseline values for glycerol obtained in the present study correspond closely to the ones available in the literature (16, 17, 37, 41). The observation that glycerol concentrations (and presumably the rate of lipolysis) in males are elevated in abdominal subcutaneous adipose tissue compared with peripheral tissue is also compatible with previous findings (21, 22). On this background, it is debatable whether GH has any preferential effects on abdominal fat; it could be argued that in relative terms the increments in glycerol concentrations in the abdomen are not different from the femoral changes. In both tissues, 1.3- to 1.5-fold increases of baseline values were seen, and, since the degree of increase over basal was the same in both tissues, the sensitivity to GH may be said to be the same. On the other hand, the absolute response was two- to threefold more pronounced in the abdomen; to the extent that this exaggerated glycerol response reflects an equally exaggerated stimulation of local lipolysis, these metabolic effects of GH will lead to preferential loss of abdominal subcutaneous fat. Thus the intracellular events that take place after binding to the GH receptor seem to be amplified in abdominal adipose tissue compared with femoral adipose tissue. In this respect, GH resembles catecholamines, which have also been reported to have distinct lipolytic effects on the abdominal depots (5, 44, 45).
Recently, the decisive role of subcutaneous abdominal fat in determining insulin sensitivity and perhaps thereby the risk of future cardiovascular disease has been highlighted (14). The most potent endogenous activators of lipolysis in adipose tissue are catecholamines (5, 44, 45), and it is thus conceivable that the action of GH, like the action of catecholamines (6), is more pronounced in abdominal than in femoral subcutaneous adipose tissue, consistent with the theory that substitution of GH in GH-deficient patients protects these patients from the otherwise increased risk of cardiovascular disease (38), by specifically decreasing upper body fat. It is not likely that GH exerts its action via catecholamines, since infusion of GH in humans does not affect the levels of circulating catecholamines (unpublished observations). Microdialysis in sheep has previously shown that GH increases basal lipolysis and increases the maximum lipolytic rate in the presence of catecholamines both in vivo and in vitro (9). Consistent with these findings, the action of GH on cAMP production in adipocytes is increased by catecholamines (3), and, on the other hand, GH sensitizes adipocytes to catecholamines (47), suggesting a synergistic effect of GH and catecholamines on lipolysis.
It remains uncertain how GH affects lipolysis in the intra-abdominal visceral fat. Judging from studies involving computed tomography scans of the abdomen in GHD patients and normal adults before and after GH treatment, GH appears to have at least the same lipolytic potential viscerally as subcutaneously (7, 24, 26).
It is well known that circulating levels of FFA are elevated in poorly regulated diabetes (23, 25), and, recently, circadian lipolysis has been studied in normal and diabetic individuals; the results implicate that increased nocturnal levels of GH may cause the perturbed circadian rhythm of lipid mobilization in insulin-dependent diabetes mellitus, with increased levels of glycerol during the night (16). The current study underlines the lipolytic effect of GH and provides additional evidence that GH is a key component in the regulation of lipid metabolism. Ordinarily, GH is secreted in a pulsatile fashion (18), and this pattern may be disrupted in certain pathological conditions (12, 15, 19). Although one study has suggested that pulsatile exposure to GH is necessary for maximum lipolytic effect (8), other protocols have found evidence of strong lipolytic effects of GH after constant infusion (28), and it therefore remains to be determined whether pulsatile GH delivery per se augments the lipolytic properties of the hormone.
In summary, we have shown that a physiological pulse of GH increases interstitial glycerol, and presumably lipolysis, in adipose subcutaneous tissue, with the absolute response being more pronounced in abdominal than in femoral adipose tissue. The study underlines the potent lipolytic effect of a pulse of GH and places GH as a strong contender among hormones regulating the rate of lipolysis.
![]() |
ACKNOWLEDGEMENTS |
---|
Anette Mengel is thanked for expert technical help. Novo Nordisk is thanked for the generous gift of growth hormone.
![]() |
FOOTNOTES |
---|
This study was supported by a grant from the Danish Medical Association and by a research grant from Novo Nordisk. Claus Højbjerg Gravholt was supported with a research fellowship by the University of Aarhus.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: C. Højbjerg Gravholt, Dept. of Endocrinology M, Århus Kommunehospital, Århus Univ. Hospital, DK-8000 Aarhus C, Denmark (E-mail: ch.gravholt{at}dadlnet.dk).
Received 1 March 1999; accepted in final form 9 July 1999.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Andersen, L.,
B. Dinesen,
P. N. Jorgensen,
F. Poulsen,
and
M. E. Roder.
Enzyme immunoassay for intact human insulin in serum or plasma.
Clin. Chem.
39:
578-582,
1993
2.
Argetsinger, L. S.,
G. S. Campbell,
X. Yang,
B. A. Witthuhn,
O. Silvennoinen,
J. N. Ihle,
and
C. Carter-Su.
Identification of JAK2 as a growth hormone receptor-associated tyrosine kinase.
Cell
74:
237-244,
1993[Medline].
3.
Argetsinger, L. S.,
and
C. Carter-Su.
Mechanism of signaling by growth hormone receptor.
Physiol. Rev.
76:
1089-1107,
1996
4.
Arner, P.,
and
J. Bolinder.
Microdialysis of adipose tissue.
J. Intern. Med.
230:
381-386,
1991[Medline].
5.
Arner, P.,
J. Bolinder,
A. Eliasson,
A. Lundin,
and
U. Ungerstedt.
Microdialysis of adipose tissue and blood for in vivo lipolysis studies.
Am. J. Physiol.
255 (Endocrinol. Metab. 18):
E737-E742,
1988
6.
Arner, P.,
E. Kriegholm,
P. Engfeldt,
and
J. Bolinder.
Adrenergic regulation of lipolysis in situ at rest and during exercise.
J. Clin. Invest.
85:
893-898,
1990[Medline].
7.
Bengtsson, B. A.,
S. Eden,
L. Lonn,
H. Kvist,
A. Stokland,
G. Lindstedt,
I. Bosaeus,
J. Tolli,
L. Sjostrom,
and
O. G. Isaksson.
Treatment of adults with growth hormone (GH) deficiency with recombinant human GH.
J. Clin. Endocrinol. Metab.
76:
309-317,
1993[Abstract].
8.
Cersosimo, E.,
F. Danou,
M. Persson,
and
J. M. Miles.
Effects of pulsatile delivery of basal growth hormone on lipolysis in humans.
Am. J. Physiol.
271 (Endocrinol. Metab. 34):
E123-E126,
1996
9.
Doris, R. A.,
G. E. Thompson,
E. Finley,
E. Kilgour,
M. D. Houslay,
and
R. G. Vernon.
Chronic effects of somatotropin treatment on response of subcutaneous adipose tissue lipolysis to acutely acting factors in vivo and in vitro.
J. Anim. Sci.
74:
562-568,
1996
10.
Ferrannini, E.
The theoretical bases of indirect calorimetry: a review.
Metabolism
37:
287-301,
1988[Medline].
11.
Gaur, S.,
M. E. Morton,
G. P. Frick,
and
H. M. Goodman.
Growth hormone regulates the distribution of L-type calcium channels in rat adipocyte membranes.
Am. J. Physiol.
275 (Cell Physiol. 44):
C505-C514,
1998
12.
Giustina, A.,
T. Scalvini,
C. Tassi,
P. Desenzani,
C. Poiesi,
W. B. Wehrenberg,
A. D. Rogol,
and
J. D. Veldhuis.
Maturation of the regulation of growth hormone secretion in young males with hypogonadotropic hypogonadism pharmacologically exposed to progressive increments in serum testosterone.
J. Clin. Endocrinol. Metab.
82:
1210-1219,
1997
13.
Goodman, H. M.,
E. Gorin,
Y. Schwartz,
L. R. Tai,
S. R. Chipkin,
T. W. Honeyman,
G. P. Frick,
and
H. Yamaguchi.
Cellular effects of growth hormone on adipocytes.
Chin. J. Physiol.
34:
27-44,
1991[Medline].
14.
Goodpaster, B. H.,
F. L. Thaete,
J. A. Simoneau,
and
D. E. Kelley.
Subcutaneous abdominal fat and thigh muscle composition predict insulin sensitivity independently of visceral fat.
Diabetes
46:
1579-1585,
1997[Abstract].
15.
Gravholt, C. H.,
J. D. Veldhuis,
and
J. S. Christiansen.
Increased disorderliness and decreased mass and daily rate of endogenous growth hormone secretion in adult Turner syndrome: the impact of body composition, physical fitness and treatment with sex hormones.
Growth Horm. IGF Res.
8:
289-298,
1998.[Medline]
16.
Hagstrom-Toft, E.,
J. Bolinder,
U. Ungerstedt,
and
P. Arner.
A circadian rhythm in lipid mobilization which is altered in IDDM.
Diabetologia
40:
1070-1078,
1997[Medline].
17.
Hagstrom-Toft, E.,
S. Enoksson,
E. Moberg,
J. Bolinder,
and
P. Arner.
Absolute concentrations of glycerol and lactate in human skeletal muscle, adipose tissue, and blood.
Am. J. Physiol.
273 (Endocrinol. Metab. 36):
E584-E592,
1997
18.
Hartman, M. L.,
A. C. Faria,
M. L. Vance,
M. L. Johnson,
M. O. Thorner,
and
J. D. Veldhuis.
Temporal structure of in vivo growth hormone secretory events in humans.
Am. J. Physiol.
260 (Endocrinol. Metab. 23):
E101-E110,
1991
19.
Hartman, M. L.,
S. M. Pincus,
M. L. Johnson,
D. H. Matthews,
L. M. Faunt,
M. L. Vance,
M. O. Thorner,
and
J. D. Veldhuis.
Enhanced basal and disorderly growth hormone secretion distinguish acromegalic from normal pulsatile growth hormone release.
J. Clin. Invest.
94:
1277-1288,
1994[Medline].
20.
Ikkos, D.,
R. Luft,
and
C. A. Gemzell.
The effect of human growth hormone in man.
Lancet
1:
720-721,
1958.
21.
Jansson, P. A.,
A. Larsson,
U. Smith,
and
P. Lonnroth.
Glycerol production in subcutaneous adipose tissue in lean and obese humans.
J. Clin. Invest.
89:
1610-1617,
1992[Medline].
22.
Jansson, P. A.,
U. Smith,
and
P. Lonnroth.
Interstitial glycerol concentration measured by microdialysis in two subcutaneous regions in humans.
Am. J. Physiol.
258 (Endocrinol. Metab. 21):
E918-E922,
1990
23.
Jensen, M. D.,
M. Caruso,
V. Heiling,
and
J. M. Miles.
Insulin regulation of lipolysis in nondiabetic and IDDM subjects.
Diabetes
38:
1595-1601,
1989[Abstract].
24.
Johannsson, G.,
P. Marin,
L. Lonn,
M. Ottosson,
K. Stenlof,
P. Bjorntorp,
L. Sjostrom,
and
B. A. Bengtsson.
Growth hormone treatment of abdominally obese men reduces abdominal fat mass, improves glucose and lipoprotein metabolism, and reduces diastolic blood pressure.
J. Clin. Endocrinol. Metab.
82:
727-734,
1997
25.
Johansen, K.,
and
A. P. Hansen.
Diurnal serum growth hormone levels in poorly and well-controlled juvenile diabetics.
Diabetes
20:
239-245,
1971[Medline].
26.
Jorgensen, J. O.,
S. A. Pedersen,
L. Thuesen,
J. Jorgensen,
H. T. Ingemann,
N. E. Skakkebaek,
and
J. S. Christiansen.
Beneficial effects of growth hormone treatment in GH-deficient adults.
Lancet
1:
1221-1225,
1989[Medline].
27.
Larsen, O. A.,
N. A. Lassen,
and
F. Quaade.
Blood flow through human adipose tissue determined with radioactive xenon.
Acta Physiol. Scand.
66:
337-345,
1966[Medline].
28.
Laursen, T.,
J. O. Jorgensen,
G. Jakobsen,
B. L. Hansen,
and
J. S. Christiansen.
Continuous infusion versus daily injections of growth hormone (GH) for 4 weeks in GH-deficient patients.
J. Clin. Endocrinol. Metab.
80:
2410-2418,
1995[Abstract].
29.
Lloyd, B.,
J. Burrin,
P. Smythe,
and
K. G. Alberti.
Enzymic fluorometric continuous-flow assays for blood glucose, lactate, pyruvate, alanine, glycerol, and 3-hydroxybutyrate.
Clin. Chem.
24:
1724-1729,
1978
30.
Lonnroth, P.,
P. A. Jansson,
and
U. Smith.
A microdialysis method allowing characterization of intercellular water space in humans.
Am. J. Physiol.
253 (Endocrinol. Metab. 16):
E228-E231,
1987
31.
Lonnroth, P.,
and
L. Strindberg.
Validation of the "internal reference technique" for calibrating microdialysis catheters in situ.
Acta Physiol. Scand.
153:
375-380,
1995[Medline].
32.
Markussis, V.,
S. A. Beshyah,
C. Fisher,
P. Sharp,
A. N. Nicolaides,
and
D. G. Johnston.
Detection of premature atherosclerosis by high-resolution ultrasonography in symptom-free hypopituitary adults.
Lancet
340:
1188-1192,
1992[Medline].
33.
Moller, N.,
J. O. Jorgensen,
O. Schmitz,
J. Moller,
J. S. Christiansen,
K. G. Alberti,
and
H. Orskov.
Effects of a growth hormone pulse on total and forearm substrate fluxes in humans.
Am. J. Physiol.
258 (Endocrinol. Metab. 21):
E86-E91,
1990
34.
Moller, N.,
O. Schmitz,
N. Porksen,
J. Moller,
and
J. O. Jorgensen.
Dose-response studies on the metabolic effects of a growth hormone pulse in humans.
Metabolism
41:
172-175,
1992[Medline].
35.
Orskov, H.,
H. G. Thomsen,
and
H. Yde.
Wick chromatography for rapid and reliable immunoassay of insulin, glucagon and growth hormone.
Nature
219:
193-195,
1968[Medline].
36.
Raben, M. S.,
and
C. H. Hollenberg.
Effect of growth hormone on plasma fatty acids.
J. Clin. Invest.
38:
484-488,
1959.
37.
Rosdahl, H.,
K. Hamrin,
U. Ungerstedt,
and
J. Henriksson.
Metabolite levels in human skeletal muscle and adipose tissue studied with microdialysis at low perfusion flow.
Am. J. Physiol.
274 (Endocrinol. Metab. 37):
E936-E945,
1998
38.
Rosen, T.,
and
B. A. Bengtsson.
Premature mortality due to cardiovascular disease in hypopituitarism.
Lancet
336:
285-288,
1990[Medline].
39.
Rosenbaum, M.,
J. M. Gertner,
N. Gidfar,
J. Hirsch,
and
R. L. Leibel.
Effects of systemic growth hormone (GH) administration on regional adipose tissue in children with non-GH-deficient short stature.
J. Clin. Endocrinol. Metab.
75:
151-156,
1992[Abstract].
40.
Rosenthal, M. J.,
and
W. F. Woodside.
Nocturnal regulation of free fatty acids in healthy young and elderly men.
Metabolism
37:
645-648,
1988[Medline].
41.
Samra, J. S.,
C. L. Ravell,
S. L. Giles,
P. Arner,
and
K. N. Frayn.
Interstitial glycerol concentration in human skeletal muscle and adipose tissue is close to the concentration in blood.
Clin. Sci. (Colch.)
90:
453-456,
1996[Medline].
42.
Scheller, D.,
and
J. Kolb.
The internal reference technique in microdialysis: a practical approach to monitoring dialysis efficiency and to calculating tissue concentration from dialysate samples.
J. Neurosci. Methods
40:
31-38,
1991[Medline].
43.
Simonsen, L.,
J. Bulow,
A. Astrup,
J. Madsen,
and
N. J. Christensen.
Diet-induced changes in subcutaneous adipose tissue blood flow in man: effect of beta-adrenoceptor inhibition.
Acta Physiol. Scand.
139:
341-346,
1990[Medline].
44.
Stallknecht, B.,
J. Bulow,
E. Frandsen,
and
H. Galbo.
Desensitization of human adipose tissue to adrenaline stimulation studied by microdialysis.
J. Physiol. (Lond.)
500:
271-282,
1997[Abstract].
45.
Stallknecht, B.,
L. Simonsen,
J. Bulow,
J. Vinten,
and
H. Galbo.
Effect of training on epinephrine- stimulated lipolysis determined by microdialysis in human adipose tissue.
Am. J. Physiol.
269 (Endocrinol. Metab. 32):
E1059-E1066,
1995
46.
Vahl, N.,
N. Moller,
T. Lauritzen,
J. S. Christiansen,
and
J. O. Jorgensen.
Metabolic effects and pharmacokinetics of a growth hormone pulse in healthy adults: relation to age, sex, and body composition.
J. Clin. Endocrinol. Metab.
82:
3612-3618,
1997
47.
Watt, P. W.,
E. Finley,
S. Cork,
R. A. Clegg,
and
R. G. Vernon.
Chronic control of the beta- and alpha 2-adrenergic systems of sheep adipose tissue by growth hormone and insulin.
Biochem. J.
273:
39-42,
1991[Medline].
48.
Yip, R. G.,
and
H. M. Goodman.
Growth hormone and dexamethasone stimulate lipolysis and activate adenylyl cyclase in rat adipocytes by selectively shifting Gi alpha2 to lower density membrane fractions.
Endocrinology
140:
1219-1227,
1999