1 Department of Clinical Physiology, Bispebjerg Hospital, DK-2400 Copenhagen NV; and 2 Department of Medical Physiology, The Panum Institute, and Copenhagen Muscle Research Centre, Rigshospitalet, DK-2200 Copenhagen N, Denmark
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ABSTRACT |
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We studied eight
normal-weight male subjects to examine whether the lipolytic rate of
deep subcutaneous and preperitoneal adipose tissues differs from that
of superficial abdominal subcutaneous adipose tissue. The lipolytic
rates in the superficial anterior and deep posterior subcutaneous
abdominal adipose tissues and in the preperitoneal adipose tissue in
the round ligament were measured by microdialysis and 133Xe
washout under basal, postabsorptive conditions and during intravenous epinephrine infusion (0.15 nmol · kg1 · min
1). Both in
the basal state and during epinephrine stimulation, the superficial
subcutaneous adipose tissue had higher interstitial glycerol
concentrations than the two other depots. Similarly, the calculated
glycerol outputs from the superficial depot were significantly higher
than those from the deep subcutaneous and the preperitoneal depots.
Thus, it is concluded that the lipolytic rate of the superficial
subcutaneous adipose tissue on the anterior abdominal wall is higher
than that of the deep subcutaneous adipose tissue on the posterior
abdominal wall and that of the preperitoneal adipose tissue in the
round ligament.
epinephrine; glycerol; microdialysis
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INTRODUCTION |
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IN HUMANS, MOST STUDIES OF LIPID METABOLISM in adipose tissue in vivo have been performed in the anterior abdominal, subcutaneous depot either by the microdialysis technique or by an arteriovenous catherization (direct Fick) technique (11). In a recent study (6), it was suggested that abdominal subcutaneous adipose tissue anatomically can be divided into two physiologically different layers (above and below Scarpa's fascia). In this study, indirect evidence was found indicating that the deep abdominal, subcutaneous layer behaves metabolically like the intra-abdominal fat depots, because the amount of fat located in each of these two sites correlates similarly with insulin resistance. In another study, Misra et al. (8) showed that the subcutaneous adipose tissue on the posterior abdominal wall is more strongly associated with insulin resistance than the subcutaneous adipose tissue on the anterior abdominal wall. Seen in the light of these findings, it may be questioned whether the anterior superficial depot has a lipolytic rate comparable to that of the deep posterior depot. In an anthropometric study using ultrasonography for assessment of the ratio between the thickness of the preperitoneal fat and that of the overlying subcutaneous fat, it was shown that this ratio was positively correlated with the visceral fat mass, implying that the masses of the preperitoneal and visceral depots vary in parallel. Thus there is some indirect evidence that the preperitoneal and visceral fat depots might have common metabolic properties (13).
Many studies have linked visceral obesity with the development of non-insulin-dependent diabetes mellitus and cardiovascular disease (7). It has been proposed that a plausible mechanism behind this linkage is an increased release of nonesterified fatty acids from the visceral depots into the portal circulation. However, the metabolism of the visceral adipose tissue depots has not been studied directly in humans under physiological conditions, because the depots are not easily accessible by catheterization techniques and cannot be subjected to microdialysis either. Therefore, it would be of interest to identify an adipose tissue depot accessible for in vivo studies with metabolic characteristics like the visceral adipose tissue. Two such depots, both easily accessible for studies with the microdialysis technique, are the preperitoneal adipose tissue depot and the subcutaneous, abdominal depot below the fascia of Scarpa.
Thus the aim of the present study was to examine the in vivo lipolytic response to epinephrine in preperitoneal as well as both superficial and deep, abdominal subcutaneous adipose tissue to elucidate whether the deep abdominal subcutaneous adipose tissue and the preperitoneal adipose tissue have higher lipolytic activity than the superficial subcutaneous abdominal depot.
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MATERIALS AND METHODS |
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Subjects.
Eight healthy males participated in the study (Table
1). The subjects were given written and
oral description of the study according to the Declaration of Helsinki
II, and their informed consent was obtained. The study was approved by
The Ethical Committee for Medical Research of Copenhagen [(KF)
01-170/00].
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Experimental protocol.
About 2 wk before the experimental day, subjects were scanned by
dual-energy X-ray absorptiometry to determine lean body mass and fat
mass (Lunar DPX-IQ, software version 4.6c, Madison, WI) (Table 1). On
the day before the experiment, subjects avoided strenuous physical
activity. After an overnight fast and abstinence from all drinks except
water, the subjects were brought to the laboratory at 8 AM and had
microdialysis, venous, and arterial catheters inserted. Then perfusion
of the microdialysis probes was started, and after a 60-min
equilibration period, the experiment was initiated. The experiment
consisted of a 60-min basal (time 0-60 min) and a 90-min (time
60-150 min) epinephrine infusion period. Epinephrine was infused
at a rate of 0.15 nmol · kg1 · min
1. During
the experiments, subjects wore light clothes and rested supine at a
room temperature of ~24°C.
Microdialysis.
Microdialysis was performed principally as described previously
(12). After anesthesia (0.4 ml lidocaine, 10 mg/ml) of the skin and linea alba at the site of perforation, a microdialysis catheter (CMA 60, CMA/Microdialysis, Stockholm, Sweden) was placed in
the preperitoneal adipose tissue by perforating the skin and abdominal
wall ~3 cm below the processus xiphoideus and by introducing the
catheter into the round ligament in the cranial direction. The catheter
was inserted during ultrasound guidance using a 7.5 MHz linear-array
transducer (Sonoline Elegra ultrasound system, Siemens Medical Systems,
Issaqua, WA). A schematic drawing of a typical ultrasound image showing
the position of the preperitoneal adipose tissue depot in relation to
the other tissue types in the region is shown in Fig.
1. After anesthesia of the skin (0.1 ml
lidocaine, 10 mg/ml) at the site of perforation, a microdialysis probe
was placed superficially in the subcutaneous adipose tissue of the
anterior abdominal wall in the periumbilical region. Another probe was
inserted in the subcutaneous adipose tissue below Scarpa's fascia in
the posterior abdominal wall at the level of the iliac crest in the
posterior axillary line. Catheters were inserted during ultrasound
guidance with care taken that they were placed above and below the
Scarpa's fascia, respectively. The catheters were perfused at a rate
of 2 µl/min with Ringer acetate with 2 mM glucose and 1.5 µM
[3H]glycerol (specific activity 7.4 GBq/mmol: NEN) by use
of a high-precision syringe pump (CMA 100, CMA/Microdialysis). The in
vivo relative recovery (RR) for glycerol was determined by the internal
reference calibration technique (9). Microdialysate was
collected in 200-µl capped microvials in 15-min periods and kept at
20°C until further analysis. Dialysate sampling was delayed by 2 min relative to sampling of arterial blood to compensate for the
transit time in the microdialysis probes. Dialysate glycerol
concentrations were determined by a CMA 600 microdialysis analyzer
(CMA/Microdialysis), each value representing a single
determination. [3H]glycerol was measured in perfusate and
dialysate by liquid scintillation counting (2200CA, Packard
Instruments). RR values (means ± SE) in superficial and deep
subcutaneous adipose tissue and in preperitoneal adipose tissue were
0.36 ± 0.02, 0.45 ± 0.01, and 0.43 ± 0.02, respectively. The RR value in superficial subcutaneous adipose tissue
was lower than RR values in preperitoneal and deep subcutaneous adipose
tissue (P < 0.05).
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Catheterization. In local analgesia (1 ml lidocaine, 10 mg/ml), a catheter (Ohmeda, Swindom, UK) was introduced percutaneously in the radial artery in the nondominant arm for blood sampling and continuous monitoring of blood pressure and heart rate (MX9504; Medex Medical, Lancashire, UK). The catheter was kept patent by regular flushing of isotonic saline. Additionally, the subjects had a catheter (Venflon, Viggo, Sweden) inserted in a forearm vein for infusion of epinephrine.
Blood flow.
Preperitoneal and both superficial and deep subcutaneous adipose tissue
blood flows were measured by the local 133Xe-washout
technique, as described previously (10). About 2 MBq of
133Xe dissolved in 0.1 ml of isotonic sodium chloride were
injected during ultrasound guidance into the preperitoneal and deep
subcutaneous adipose tissues according to positions of
microdialysis catheters, whereas ~1 MBq of 133Xe
dissolved in 0.05 ml of isotonic sodium chloride was injected into the
superficial subcutaneous adipose tissue. Washout of 133Xe
was registered by a Mediscint system (Oakfield Instruments, Oxford,
UK). The calculation of adipose tissue blood flow was performed, as
described previously, with an average tissue-to-blood partition
coefficient value () of 8 ml/g in all adipose tissue depots
(2).
Blood sampling and analyses. Blood for determination of metabolites and hormones was sampled in 0°C-cooled vials from the radial artery and immediately centrifuged. Blood was sampled at 9, 24, 39, and 54 min in the basal period and at 69, 84, 99, 114, 129, and 144 min during epinephrine infusion. Blood for determination of glycerol was measured in neutralized, deproteinized extracts of whole blood (3). Blood for determination of catecholamines was stabilized with reduced glutathione and heparin, and plasma catecholamine concentrations were determined by a single-isotope radioenzymatic assay (1).
Calculations.
From the interstitial glycerol concentration, the concentration
in venous blood water (Cv calc) was calculated by the
principle described by Intaglietta and Johnson (4). Blood
water flow was calculated as {[(1 hematocrit) · 0.94 + (hematocrit · 0.67)] · blood flow}, measured by the
133Xe washout. Adipose tissue glycerol output was
calculated as the product of the blood water flow and the difference
between Cv calc and the concentration in arterial blood water.
Statistics. All data are presented as means ± SE. A two-way repeated-measures ANOVA was used to test whether interstitial glycerol concentrations, glycerol outputs, and blood flows differed with time or among adipose tissues. A one-way ANOVA was used to test whether blood pressure, heart rate, hematocrit, and hormone concentrations differed with time. The Student-Newman-Keuls test was used as a post hoc test. A significance level of 0.05 in two-tailed testing was chosen a priori.
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RESULTS |
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Hormone concentrations. Epinephrine infusion increased epinephrine concentration in arterial plasma from 0.31 ± 0.05 nM in the basal state to 4.00 ± 0.18 nM (P < 0.05). Norepinephrine concentration in arterial plasma did not change significantly with epinephrine infusion (basal state: 1.08 ± 0.10 nM; during epinephrine: 1.23 ± 0.16 nM).
Whole body. Epinephrine infusion increased heart rate (50 ± 2 vs. 60 ± 2 beats/min) significantly. Systolic blood pressure was increased (126 ± 4 vs. 135 ± 5 mmHg; P < 0.05), whereas diastolic blood pressure (63 ± 2 vs. 59 ± 3 mmHg) was essentially unchanged, with epinephrine infusion. Hematocrit did not change with time (43 ± 0 vs. 44 ± 0%).
Adipose tissue blood flow.
Adipose tissue blood flows increased significantly by two- to threefold
during epinephrine infusion (Fig. 2).
During epinephrine infusion, adipose tissue blood flow levels were
significantly higher in superficial subcutaneous adipose tissue than in
preperitoneal adipose tissue.
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Arterial blood and interstitial glycerol concentrations.
Epinephrine infusion increased arterial and dialysate glycerol
concentrations, which peaked 0.5 h after start of the infusion (Fig. 3). In Fig. 3 are also given the
calculated interstitial glycerol concentrations. Both in the basal
state and during epinephrine infusion, the interstitial glycerol
concentration was significantly higher in the superficial subcutaneous
adipose tissue than in the preperitoneal and deep subcutaneous adipose
tissues.
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Calculated glycerol output. Epinephrine significantly increased glycerol output from all three depots (P < 0.05; Fig. 3). However, the output from the superficial subcutaneous adipose tissue was significantly higher than outputs from the preperitoneal and deep subcutaneous adipose tissues.
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DISCUSSION |
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The main finding in the present study is that the increase in lipolytic activity elicited by epinephrine in a high physiological concentration is higher in the anterior abdominal, superficial subcutaneous adipose tissue layer compared with the posterior abdominal, deep subcutaneous adipose tissue layer and with the preperitoneal adipose tissue in the round ligament.
The tissue-to-blood partition coefficient () for Xe was not
directly determined in each depot in this study. A value of 8 ml/g was
used for all depots, because this has been found to be the average
value in subcutaneous abdominal adipose tissue sampled randomly during
abdominal surgery in a normal-weight population with an average body
mass index (BMI) of 24 kg/m2 (2). The subjects
studied in the present experiments had an average BMI of ~25
kg/m2. Jansson and Lönnroth (5) studied
a lean population with a BMI of ~22 kg/m2 and found the
average
to be 8.6 ml/g when estimated from needle biopsies taken
from the subcutaneous, abdominal adipose tissue without distinction
between superficial and deep layers. If we assume that
is 10 ml/g
in the preperitoneal and deep subcutaneous depots,
corresponding to ~5% water content and ~90% lipid content in the
tissues, this would not change the overall pattern in the present
findings. Thus, despite the uncertainty of the assumed average
value, the present findings show that the lipolytic activity in the
superficial subcutaneous layer is higher than in the two other depots
during epinephrine infusion. Therefore, the present results support the
view that the many results published during the last decade from
studies of the anterior abdominal subcutaneous adipose tissue give a
reliable picture of adipose tissue metabolism and its regulation.
Furthermore, the study has provided direct evidence in favor of the
view that the superficial abdominal adipose tissue on the anterior
abdominal wall and the deep abdominal adipose tissue on the posterior
abdominal wall are not metabolically equal. An explanation for the
stronger association of the deep subcutaneous adipose tissue and
insulin resistance is that the major part of the subcutaneous adipose
tissue on the abdominal wall is situated below Scarpa's fascia. Thus
the deep subcutaneous tissue mass is larger than the superficial mass, giving the former layer a higher metabolic impact despite a lower metabolic rate.
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ACKNOWLEDGEMENTS |
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We thank Inge Rasmussen and Lisbeth Kall for excellent technical assistance.
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FOOTNOTES |
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This work was funded by The Novo Nordisk Foundation, The Danish Heart Foundation (97-1-3-48-22465), The John and Birthe Meyer Foundation, and The Danish National Research Foundation (504).
Address for reprint requests and other correspondence: J. Bülow, Dept. of Clinical Physiology, Bispebjerg Hospital, DK-2400 Copenhagen NV, Denmark (E-mail: jens.bulow{at}bbh.hosp.dk).
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. Section 1734 solely to indicate this fact.
Received 7 March 2001; accepted in final form 9 July 2001.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Ben-Jonathan, N,
and
Porter JC.
A sensitive radioenzymatic assay for dopamine, norepinephrine, and epinephrine in plasma and tissue.
Endocrinology
98:
1497-1507,
1976[Abstract].
2.
Bülow, J,
Jelnes R,
Astrup A,
Madsen J,
and
Vilmann P.
Tissue/blood partition coefficients for xenon in various adipose tissue depots in man.
Scand J Clin Lab Invest
47:
1-3,
1987[Medline].
3.
Bülow, J,
Simonsen L,
Wiggins D,
Humphreys SM,
Frayn KN,
Powell D,
and
Gibbons GF.
Co-ordination of hepatic and adipose tissue lipid metabolism after oral glucose.
J Lipid Res
40:
2034-2043,
1999
4.
Intaglietta, M,
and
Johnson PC.
Principles of capillary exchange.
In: Peripheral Circulation, , edited by Johnson PC. New York: Wiley, 1978, p. 141-166.
5.
Jansson, PA,
and
Lönnroth P.
Comparison of two methods to assess the tissue/blood partition coefficient for xenon in subcutaneous adipose tissue in man.
Clin Physiol
15:
47-55,
1995[ISI][Medline].
6.
Kelley, DE,
Thaete FL,
Troost F,
Huwe T,
and
Goodpaster BH.
Subdivisions of subcutaneous abdominal adipose tissue and insulin resistance.
Am J Physiol Endocrinol Metab
278:
E941-E948,
2000
7.
Kissebah, AH.
Central obesity: measurement and metabolic effects.
Diabetes Rev
5:
8-20,
1997[ISI].
8.
Misra, A,
Garg A,
Abate N,
Peshock RM,
Stray GJ,
and
Grundy SM.
Relationship of anterior and posterior subcutaneous abdominal fat to insulin sensitivity in nondiabetic men.
Obes Res
5:
93-99,
1997[Abstract].
9.
Scheller, D,
and
Kolb J.
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[ISI][Medline].
10.
Simonsen, L,
Bülow J,
Astrup A,
Madsen J,
and
Christensen NJ.
Diet-induced changes in subcutaneous adipose tissue blood flow in man: effect of beta-adrenoceptor inhibition.
Acta Physiol Scand
139:
341-346,
1999.
11.
Simonsen, L,
Bülow J,
and
Madsen J.
Adipose tissue metabolism in humans determined by vein catheterization and microdialysis techniques.
Am J Physiol Endocrinol Metab
266:
E357-E365,
1994
12.
Stallknecht, B,
Simonsen L,
Bülow J,
Vinten J,
and
Galbo H.
Effect of training on epinephrine-stimulated lipolysis determined by microdialysis in human adipose tissue.
Am J Physiol Endocrinol Metab
269:
E1059-E1066,
1995
13.
Suzuki, R,
Watanabe S,
Hirai Y,
Akiyama K,
Nishide T,
Matsushima Y,
Murayama H,
Ohshima H,
Shinomiya M,
Shirai K,
Saito Y,
Yoshida S,
Saisho H,
and
Ohto M.
Abdominal wall fat index, estimated by ultrasonography, for assessment of the ratio of visceral fat to subcutaneous fat in the abdomen.
Am J Med
95:
309-314,
1993[ISI][Medline].