Cyclic AMP-dependent and independent inhibition of lipolysis by adenosine and decreased pH.

NA-stimulated lipolysis and cAMP formation in isolated rat fat cells is inhibited by acidosis. In the present report we have examined the quantitative relationship between lipolysis and cAMP formation at normal and reduced pH and the possible involvement of adenosine, an endogenous inhibitor of cAMP formation. Adenosine antagonized cAMP accumulation and to a considerably lower degree lipolysis, effects potentiated by acidosis. Theophylline, an antagonist of adenosine effects, stimulated lipolysis and cAMP-accumulation, and potentiated responses to NA. Adenosine deaminase (ADA) had theophylline-like effects. Acidosis inhibited lipolysis and cAMP accumulation induced by ADA and theophylline to a larger extent than those induced by NA. It is suggested that adenosine modulates fat cell cAMP production and may contribute to the antilipolytic effect of acidosis. There was a curvilinear relationship between cAMP elevation and glycerol production in fat cell suspensions, which was different at pH 7.4 and at pH 6.6. The amount of cAMP needed for half-maximal activation of lipolysis increased from 1.3 (pH 7.4) to 3.1 pMol X 10(-5) cells (pH 6.6). The maximal glycerol production was reduced from 1 300 to 900 nMol X 10(-5) cells. The antilipolytic effect of acidosis is apparently due partly to an inhibition of cAMP formation and partly to inhibition of subsequent step(s) in the activation sequence.     

Inhibition by Acidosis of Adenosine 3‘,5’-Cyclic Monophosphate Accumulation and Lipolysis in Isolated Rat Fat Cells1

Lipolysis and cyclic AMP accumulation were studied in isolated rat fat cells at normal (7.4) and decreased (7.0, 6.6) pH. Acidosis inhibited lipolysis and cyclic AMP accumulation due to NA non-competetively. Maximal lipolysis (3 μM NA) was inhibited by 25% at pH 7.0 and by 61 % at pH 6.6. Cyclic AMP accumulation 5 min after 3 μM NA was inhibited by 57% at pH 7.0 and by 83% at pH 6.6. Between 10 and 60 minutes of incubation NA-stimulated lipolysis was linear at pH 7.4, whereas a progressively increasing inhibition was seen at lower pH. The FFA production was inhibited to the same degree as glycerol production by acidosis. The fraction of FFA associated with the cells was the same at all pHs. Thus, we have no evidence that acidosis inhibits lipolysis via accumulation of FFA intracellularly. NA-induced accumulation of ³H-cAMP from ³H-ATP, endogenously formed by prelabelling the cells with ³H-adenine, was inhibited by acidosis both in the presence and absence of theophylline in the incubation medium (by 48 and 44% respectively at pH 7.0 and by 74 and 68 % at pH 6.6). Cyclic nucleotide phosphodiesterase in homogenates of fat cells was inhibited by decreasing the pH, whether measured at high or low substrate concentrations. Basal adenylyl cyclase activity in a cell membrane fraction from fat cells was affected to a minor degree, while NA-stimulated activity was inhibited by decreased pH. The response to 3 μM NA at pH 6.6 was inhibited by 43% relative to control. The results show that acidosis inhibits NA-induced cyclic AMP accumulation by interfering with the formation, rather than the inactivation of the nucleotide. Since NA-induced lipolysis is a cyclic AMP-mediated process it is suggested that at least part of the antilipolytic effect of acidosis is due to inhibition of cyclic AMP formation.     

Inhibition by acidosis of adenosine 3',5'-cyclic monophosphate accumulation and lipolysis in isolated rat fat cells.

Lipolysis and cyclic AMP accumulation were studied in isolated rat fat cells at normal (7.4) and decreased (7.0, 6.6) pH. Acidosis inhibited lipolysis and cyclic AMP accumulation due to NA non-competetively. Maximal lipolysis (3 muM NA) was inhibited by 25% at pH 7.0 and by 61% at pH 6.6 Cyclic AMP accumulation 5 min after 3 muM NA was inhibited by 57% at pH 7.0 and by 83% at pH 6.6. Between 10 and 60 minutes of incubation NA-stimulated lipolysis was linear at pH 7.4, whereas a progressively increasing inhibition was seen at lower pH. The FFA production was inhibited to the same degree as glycerol production by acidosis. The fraction of FFA associated with the cells was the same at all pHs. Thus, we have no evidence that acidosis inhibits lipolysis via accumulation of FFA intracellularly. NA-induced accumulation of 3H-cAMP from 3H-ATP, endogenously formed by prelabelling the cells with 3H-adenine, was inhibited by acidosis both in the presence and absence of theophylline in the incubation medium (by 48 and 44% respectively at pH 7.0 and by 74 and 68% at pH 6.6). Cyclic nucleotide phosphodiesterase in homogenates of fat cells was inhibited by decreasing the pH, whether measured at high or low substrate concentrations. Basal adenylyl cyclase activity in a cell membrane fraction from fat cells was affected to a minor degree, while NA-stimulated activity was inhibited by decreased pH. The response to 3 muM NA at pH 6.6 was inhibited by 43% relative to control. The results show that acidosis inhibits NA-induced cyclic AMP accumulation by interfering with the formation, rather than the inactivation of the nucleotide. Since NA-induced lipolysis is a cyclic AMP-mediated process it is suggested that at least part of the antilipolytic effect of acidosis is due to inhibition of cyclic AMP formation.     

Direct Antilipolytic Effect of Acidosis in Isolated Rat Adipocytes

The possibility that acidosis inhibits lipolysis indirectly by causing ionic shifts or by favouring the accumulation of an inhibitor has been tested in isolated fat cells. Lipolysis induced by 3 μM noradrenaline (NA) was inhibited by 40–60% and that induced by 1 mM theophylline (THEO) by about 75% when the pH was reduced to 6.6. Lipolysis induced by NA+THEO was inhibited by 20–30%. Changing the concentration of Ca⁺⁺or Mg⁺⁺did not alter the degree of inhibition. Reducing the K⁺-ion concentration enhanced the inhibitory effect of low pH on lipolysis induced by NA or NA + THEO, whereas cyclic AMP accumulation was uninfluenced. Omitting glucose from the incubation medium caused a slight enhancement of pH-induced inhibition of lipolysis (from 60 to 70%, p<0.01). Reducing the concentration of albumin, which binds inhibitory substances such as FFA, reduced lipolysis more at normal than at reduced pH. At high FFA/albumin ratios (5 or above) lipolysis was similar at normal and reduced pH. The antilipolytic effect of decreased pH was equally pronounced in perifused fat cells, where inhibitory substances are not allowed to accumulate. Our results suggest that the antilipolytic effect of acidosis is mainly a direct effect of the increase in H⁺ion concentration. The inhibitory effect of acidosis on various responses to β-adrenoceptor stimulation may be caused by a decreased formation of cyclic AMP in turn caused directly by the decrease in pH.     

Influence of Adipose Tissue Blood Flow on the Lipolytic Response to Circulating Noradrenaline at Normal and Reduced pH

Hypercapnic acidosis (pH 7.0) inhibits the lipolytic response of canine subcutaneous adipose tissue to i.v. infused noradrenaline (NA) by 80 per cent or more. The response to sympathetic nerve stimulation, on the other hand, is only reduced by 1040 per cent during acidosis. The fate of intravenously infused ³H-labelled NA (0.35 ug × kg^-1× min^-1 for 30 min) was not significantly altered by acidosis. The rate of disappearance of unmetabolized NA from the arterial plasma after an infusion was the same at pH 7.4 and 7.0 and the calculated increase in circulating NA during infusions was 4 ng/ml at both pH:s. I.v. infusion of Na increases adipose tissue blood flow, an effect which is attenuated by acidosis. There was a significant correlation (p< 0.001) between adipose tissue blood flow and the lipolytic response at normal pH. Preventing the NA-induced increase in blood flow by constant flow perfusion reduced the lipolytic response at normal pH. The degree of inhibition by acidosis of the lipolytic response to i.v. NA was significantly reduced (from 79 to 56 per cent, p < 0.05) when the adipose tissue was perfused at constant flow. These data suggest that adipose tissue blood flow is important in determining the lipolytic response to i.v. NA, probably by influencing the delivery of NA to the tissue. The marked inhibition by acidosis of lipolysis due to i.v. infused NA therefore appears to be the combined effect of a direct antilipolytic effect of acidosis and a decreased delivery of N A to the adipose tissue due to the attenuated blood flow response.     

Direct antilipolytic effect of acidosis in isolated rat adipocytes.

The possibility that acidosis inhibits lipolysis indirectly by causing ionic shifts or by favouring the accumulation of an inhibitor has been tested in isolated fat cells. Lipolysis induced by 3 muM noradrenaline (NA) was inhibited by 40-60% and that induced by 1 mM theophylline (THEO) by about 75% when the pH was reduced to 6.6. Lipolysis induced by NA + THEO was inhibited by 20-30%. Changing the concentration of Ca++ or Mg++ did not alter the degree of inhibition. Reducing the K+-ion concentration enhanced the inhibitory effect of low pH on lipolysis induced by NA or NA + THEO, whereas cyclic AMP accumulation was uninfluenced. Omitting glucose from the incubation medium caused a slight enhancement of pH-induced inhibition of lipolysis (from 60 to 70%, p less than 0.01). Reducing the concentration of albumin, which binds inhibitory substances such as FFA, reduced lipolysis more at normal than at reduced pH. At high FFA/albumin ratios (5 or above) lipolysis was similar at normal and reduced pH. The antilipolytic effect of decreased pH was equally pronounced in perifused fat cells, where inhibitory substances are not allowed to accumulate. Our results suggest that the antilipolytic effect of acidosis is mainly a direct effect of the increase in H+ ion concentration. The inhibitory effect of acidosis on various responses to beta-adrenoceptor stimulation may be caused by a decreased formation of cyclic AMP in turn caused directly by the decrease in pH.     

The antilipolytic effect of endogenous and exogenous adenosine in canine adipose tissue in situ

The effects of adenosine, 2-Cl-adenosine, two adenosine uptake inhibitors (dipyridamole and dilazep) and the adenosine deaminase (ADA) inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) were studied on basal and stimulated lipolysis in subcutaneous adipose tissue. The basal lipolysis was unaffected by all agents. Lipolysis induced by nerve stimulation (4 Hz, 5 min) was dose-dependently antagonized (up to 100%) by close i.a. infusions of adenosine (1–40 μM in blood); if the nerve induced vasoconstriction was prevented by α-adrenoceptor-blockade. 2-Cl-adenosine was a more potent antilipolytic agent than adenosine. EHNA (3–10 μM in blood) did not inhibit stimulated lipolysis in vivo possibly because of the low ADA activity in fat cells. Dipyridamole (0.5-1.5 μM in blood) in combination with EHNA increased the venous plasma concentration of adenosine from 0.3±0.05 to 0.7±0.1 μM and enhanced the tissue concentration close to 3-fold. Lipolysis induced by nerve stimulation (4 Hz) was reduced by about 40% by dipyridamole + EHNA and that induced by close i.a. noradrenaline injection (20 nmol) by approximately 60%. It is concluded that adenosine is an antagonist of stimulated lipolysis in subcutaneous adipose tissue in situ in concentrations that are reached during prolonged sympathetic nerve stimulation.     

Uptake and release of adenosine in isolated rat fat cells

Radioactively labelled adenosine and adenine were rapidly taken up by isolated rat fat cells, and incorporated into nucleotides, of which ATP dominated. The overall process had an apparent K_m of 1–5 μM. During incubation, especially in the presence of lipolytic agents, there was a reduction in labelled ATP with a compensatory increase in ADP, AMP, cAMP and nucleosides. The build-up of adenosine during incubation was inhibited by theophylline, which inhibits 5′-nucleotidase. Radioactivity released from perifused fat cells consisted mainly of nucleoside material, of which adenosine predominated. Lipolytic stimulation caused no significant increase in nucleoside outflow from perifused cells, whereas oxygenation was capable of reducing this outflow. It is concluded that adenosine is formed by fat cells as a consequence of ATP breakdown. Stimulation of lipolysis during activation of the sympathetic nerves leads to reversible ATP breakdown and adenosine release. Adenosine might therefore act as a modulator of lipolysis in vivo under these conditions, even though it does not serve as a feed back regulator in the proper sense.     

Uptake and release of adenosine in isolated rat fat cells.

Radioactively labelled adenosine and adenine were rapidly taken up by isolated rat fat cells, and incorporated into nucleotides, of which ATP dominated. The overall process had an apparent Km of 1--5 micrometers. During incubation, especially in the presence of lipolytic agents, there was a reduction in labelled ATP with a compensatory increase in ADP, AMP, cAMP and nucleosides. The build-up of adenosine during incubation was inhibited by theophylline, which inhibits 5'-nucleotidase. Radioactivity released from perifused fat cells consisted mainly of nucleoside material, of which adenosine predominated. Lipolytic stimulation caused no significant increase in nucleoside outflow from perifused cells, whereas oxygenation was capable of reducing this outflow. It is concluded that adenosine is formed by fat cells as a consequence of ATP breakdown. Stimulation of lipolysis during activation of the sympathetic nerves leads to reversible ATP breakdown and adenosine release. Adenosine might therefore act as a modulator of lipolysis in vivo under these conditions, even though it does not serve as a feed back regulator in the proper sense.     

Adenosine potentiates the effects of LH and isoproterenol on luteal cells but not on isolated intact corpora lutea

Adenosine potentiated the stimulatory effect of luteinizing hormone (LH) in a dose-dependent way on the production of cyclic AMP (cAMP) in isolated cells from heavily luteinized rat ovaries and from individual rat corpora lutea of various ages (2- and 5-day-old). Such an effect has earlier been reported only for cells from heavily luteinized ovaries (Behrman et al. 1983). A similar potentiating effect of adenosine was now seen on catecholamine-stimulated cAMP production in isolated cells from 2-day-old corpora lutea. Adenosine did not, however, potentiate LH- or catecholamine-stimulated cAMP production in isolated intact corpora lutea.     

Effect of Prostaglandin E1 on Fat Mobilizing Lipolysis in Rat Adipose Tissue in Relation to the Nutritional Condition

The effect of prostaglandin E₁ (PGE₁) on fat mobilizing lipolysis in rat adipose tissue was studied in relation to the nutritional condition by following the release of glycerol during incubation in vitro. In fed tissues PGE₁ at concentration of 0.01, 0.1, 1 and 10 μg/ml incubation medium significantly lowered the lipolysis to 64, 41, 48 and 68% of the basal rate (average of 6 expts.). The lipolytic rate was significantly higher with 10 than with 0.1 μg/ml of PGE₁. The corresponding figures in adipose tissue from fasted rats were 90, 91, 86 and 95% respectively (average of 7 expts.). These average decreases were not statistically significant. Refeeding fasted rats with glucose one hour before the study restored the sensitivity of adipose tissue to the antilipolytic effect of PGE₁. In rat fat the nutritional condition is thus of importance for the appearance of the antilipolytic effect of PGE₁. The possible role of the tissue sensitivity to PGE₁ in regulating fat mobilizing lipolysis during fasting was discussed.     

Antilipolytic effect of adenosine in isolated perifused fat cells

Adenosine markedly inhibits cyclic AMP accumulation in isolated fat cells, whereas inhibitory effects of adenosine on lipolysis have been difficult to demonstrate. The present study has been performed on isolated “perifused” fat cells where continuous monitoring of the lipolytic rate is possible and where modulating substances, such as adenosine, are not allowed to accumulate. Adenosine deaminase was ineffective as a lipolytic agent in perifused fat cells, suggesting no important background activity of adenosine in this system. Micromolar concentrations of adenosine inhibited lipolysis induced by noradrenaline (0.3-1 μM) and theophylline (1 mM). Theophylline was an effective lipolytic agent also in perifused fat cells suggesting that antagonism of adenosine is not the major mode of action of this drug on fat cells.     

Adenosine and ATP effects on isolated guinea pig gallbladder

The effects of adenosine, ATP and several derivatives of adenosine were measured in isolated strips of guinea pig gallbladder. Adenosine caused relaxations which were antagonized by theophylline and potentiated by an inhibitor of adenosine uptake, 6-(1-hydroxy-5-nitrobenzylthio)-guanosine (HNBTG). Among several adenosine derivatives, 2-chloroadenosine and 5′-N-ethylcarboxymidoadenosine were similarly effective while 1-N⁶-phenylisopropyladenosine was only a weak relaxant. None of the derivatives caused maximal relaxations at 100 μM, and thus absolute potencies could not be determined. ATP caused predominantly contractile effects, with relaxations sometimes being evident at high concentrations. Indomethacin abolished contractile effects of ATP, suggesting prostaglandin involvement, and only relaxations were evident in its presence. Adenosine deaminase abolished the effects of adenosine and partly reduced the relaxant effects of ATP in the presence of indomethacin. In view of the low potency of adenosine and ATP, physiological roles for these compounds in gallbladder motility are not readily evident.     

Inhibition of the Lipolytic Response to Nerve Stimulation during Acidosis

Acidosis inhibits catecholamine-induced lipolysis in vivo and in vitro. The lipolytic response of canine subcutaneous adipose tissue to short (5 min) nerve stimulations at 4 Hz was, however, not influenced by hypercapnic acidosis (pH 7.0). The steady state outflow of glycerol during a prolonged nerve stimulation at 4 Hz was inhibited by 40 per cent (p<0.05) at pH 7.0. Similarly, glycerol outflow during vasodilatation induced by a 4 Hz stimulation in α-blocked adipose tissue was inhibited by 37 per cent (p<0.05). Post-stimulatory glycerol outflow was, however, not influenced by acidosis. This poststimulatory glycerol outflow, which may represent a complex wash-out phenomenon, forms the largest part of the response to short nerve stimulations. It is suggested that steady state, rather than poststimulatory lipolysis should be studied in order to see the influence of treatments such as acidosis on responses to nerve stimulation.     

Properties of adenosine deaminase from Candida albicans

Adenosine deaminase (ADA; adenosine aminohydrolase, E.C. 3.5.4.4), a purine catabolic enzyme, was studied in Candida albicans, an opportunistic yeast that causes diseases ranging from superficial infections to the deep systemic disease, candidiasis, in immunosuppressed humans. The fungus was grown as a yeast form in Lee 's synthetic medium, pH 4.5, at room temperature for various growth periods. Adenosine deaminase (ADA) activity was determined from the cell free extract by measuring the change in absorbance 265 nm resulting from the deamination of adenosine. In yeast form, maximum growth and ADA activity were found at 72 and 24 hours, respectively, whereas in the mycelial form both the growth and ADA activity were maximum after 48 hours. Among the three media tested, tryptic soy broth supported maximum growth and enzyme production, compared to Lee synthetic medium or Sabouraud dextrose broth. The enzyme was active over the pH range 4–8 and the optimum temperature for ADA activity was found to be 37 °C.     

Adenosine is not a direct GHSR agonist--artificial cross-talk between GHSR and adenosine receptor pathways

Aim: To assess if adenosine is a direct growth hormone secretagogue receptor (GHSR) agonist by investigating the mechanism behind adenosine induced calcium release in human embryonic kidney 293s (HEK) cells expressing GHSR. Methods: Calcium mobilization, cyclic adenosine monophosphate (cAMP) and IP₃ experiments were performed using HEK cells stably expressing GHSR and/or adenosine A_2B receptor (A_2BR). Results: Adenosine has been widely reported as a GHSR agonist. In our hands, adenosine and forskolin stimulated calcium release from IP₃ controlled stores in HEK–GHSR cells but not in non‐transfected HEK cells. This release was not accompanied by increased IP₃ levels. The calcium release was both cholera toxin and U73122 sensitive, indicating the involvement of both Gα_s/adenylyl cyclase and Gα_q/11/phospholipase C pathways. Importantly, the GHSR inverse agonist [D‐Arg¹ D‐Phe⁵ D‐Trp^7,9 Leu¹¹]‐Substance P (SP‐analogue) blocked the adenosine stimulated calcium release, demonstrating that GHSR is involved. Assessment of the GHSR‐dependent calcium release using adenosine receptor agonists and antagonists resulted in a rank order of potencies resembling the profile of A_2BR. A_2BR over‐expression in HEK–GHSR cells enhanced potency and efficacy of the adenosine induced calcium release without increasing IP₃ production. Moreover, A_2BR over‐expression in HEK cells potentiated NECA‐induced cAMP production. However, GHSR expression had no effect on intracellular cAMP production. Conclusion: In HEK–GHSR cells adenosine activates endogenously expressed A_2BR resulting in calcium mobilization. We hypothesize that the responsible mechanism is cAMP‐dependent sensitization of IP₃ receptors for the high basal level of IP₃ caused by GHSR constitutive activity. Altogether, our results demonstrate that adenosine is not a direct GHSR agonist.     

Hypoxia in fibroblast cultures. I. Changes in glucose consumption by 5 vol.-% oxygen concentration and reduced pH.

In secondary cultures of rat embryonic fibroblasts the glucose consumption and lactate concentration were comparatively investigated in 5 and 21 Vol.-% O2 environment at pH 6.6 and pH 7.4 (HEPES-buffer). The results were correlated with cell density. The following observations were made: 1. At pH 6.6 the rate of cell proliferation was reduced to 81%; by additional hypoxia it was reduced to 71%. 2. Increase in cell density effectuated decrease of glucose consumption and lactate production at pH 7.4 and pH 6.6 in 5% as well as in 21% O2 environment. 3. At pH 7.4 enhancement of glucose consumption and lactate production due to hypoxia can be observed only at low cell density. 4. At pH 6.6 respiration of fibroblasts was little influenced by 5% O2 environment. 5. Transition from pH 7.4/21% O2 to pH 6.6/5% O2 effectuated decrease in glucose consumption and lactate concentration in tissues in hypoxic environment. This suggests a pH-governed feedback mechanism. Abbreviations used in the text: c-AMP = cyclic adenosine monophosphate; MPS = acid mucopolysaccharides (glycosaminoglycans).     

Vascular and Metabolic Effects of Theophylline,Dibuturyl Cyclic AMP and Dibuturyl Cyclic GMP in Canine Subcutaneous Adipose Tissue in situ1

In canine subcutaneous adipose tissue theophylline (2×10^--⁴ M), cAMP and ATP (10^--⁵ M), and DBcAMP (8×10^--⁴ M) increased blood flow by by approximately 100 per cent. These compounds also antagonized sympathetic vasoconstriction. Theophylline and DBcAMP increased glycerol release dose-dependently, while cAMP and ATP were ineffective up to I mM. Theophylline (0.4–0.8 mM) potentiated the lipolytic effect of nerve stimulation, while 2–8 mM apparently caused maximal stimulation Per se. DBcAMP did not affect FFA release following nerve stimulation, while DBcGMP potentiated. The apparent rate of re-esterification, glucose uptake and lactate release was decreased by theophylline. DBcAMP (0.1–0.4 mM) had no effect on these parameters, while DBcGMP at the same concentration decreased re-esterification and lactate release. Stimulated overflow of ³H from tissues prelabelled with L-³H-noradrenaline was reduced to 50 per cent by ATP (0.1–0.4 mM), but was unaffected by DBcAMP and DBcGMP at the same concentration. The results support the view that cAMP mediates the metabolic actions of sympathetic nerve stimulation in canine subcutaneous adipose tissue. The relationship between cAMP and vascular reactions may be more complex.     

大鼠脂肪细胞TSH受体机能研究

目的：研究TSH及Graves'TgC对大鼠脂肪细胞的作用。方法：获取大鼠游离的脂肪细胞。溶脱TSH受体。采用A蛋白尾析柱纯化Graves患者的IgG以脂肪细胞内cAMP浓度及释放到孵化液中甘油浓度作为脂肪分解指标,用cAMP及甘油试剂盒测定cAMP浓度及甘油浓度。结果：1mU／ml的TSll能增加大鼠雅高脂肪细胞的cAMP浓度及甘油的释放。脓苷引起cAMP及甘油的TSH剂量依赖曲线向右移。Gare’TgG抑制[125I]-TSH结合于大鼠脂肪细胞膜上ISH受体,并能刺激雅高脂肪细胞内cAMP的形成。结论：ISH受体功能性表达于脂肪细胞,其生物学效应是通过活化腺耷环化酶而实现的。     

Regional variation of white adipocyte lipolysis during the annual cycle of the alpine marmot.

During winter, hibernating animals rely on their lipid stores for survival. In vitro lipolytic activity of isolated adipocytes from gonadal and subcutaneous white adipose tissue (WAT) was studied in captive alpine marmots (Marmota marmota) at two different times of their yearly cycle. During the summer, when marmots were eating, adipocyte responsiveness and sensitivity to isoprenaline and noradrenaline were higher in gonadal than in subcutaneous WAT. During hibernation, when marmots were spontaneously fasting. both the response and sensitivity to catecholamines decreased in gonadal WAT to the level of subcutaneous WAT. A similar pattern of response was also observed when lipolysis was stimulated with glucagon but the lipolytic rate was three times lower than with catecholamines. Adenosine deaminase (ADA) had a marked stimulatory effect on lipolysis, especially during the 'feeding' period, suggesting that adenosine may be a potent lipolytic modulator in marmot adipocytes. It is concluded that in marmots, lipolysis could be differentially regulated between fat depots during the annual cycle possibly to optimize either the building-up or the use of fat reserves.