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.     

Metabolic effects of blood flow restriction in adipose tissue.

The metabolic effects of blood flow restriction were studied in isolated blood-perfused canine subcutaneous adipose tissue. Blood flow restriction (on the average to 20 per cent of control flow) was caused by either mechanical clamping of the arterial inflow or by i.a. injections of methoxamine or angiotensin. Glucose uptake in the adipose tissue was reduced during blood flow restriction. This was partially compensated for by a period of increased glucose uptake following restoration of flow. Blood flow restriction also caused an increase in the venous lactate/pyruvate ratio. The basal lipolytic rate was decreased during blood flow restriction. Lipolysis induced by brief (5 min) sympathetic nerve stimulation (4 Hz) was not inhibited by blood flow restriction as the total amount of glycerol released from the tissue was unaffected. The outflow rate was reduced during blood flow restriction, but glycerol trapped within the tissue was apparently not reutilized by the fat cells as it was released upon flow restroation. FFA outflow following nerve stimulation was, however, inhibited suggesting increased reutilization of FFA within the tissue. This increased reutilization may ultimately be caused by the observed change in red./ox.-balance and/or by the limited carrier capacity (albumin) available during blood flow restriction. Three main conclusions may be drawn from the present results. Firstly, plasma levels of glycerol and FFA do not necessarily reflect adipose tissue lipolysis at a given moment. Secondly, the decreased adipose tissue blood flow seems to be a major cause of the lowered FFA-levels during hemorrhage. Thirdly, in contrast to hemorrhage, even severe reduction of adipose tissue blood flow is insufficient to cause irreversible ischemic damage.     

Influence of adenosine on the vascular responses to sympathetic nerve stimulation in the canine subcutaneous adipose tissue

Adenosine appears to regulate resting blood flow in canine subcutaneous adipose tissue. Sympathetic nerve stimulation has been shown to enhance the adenosine production in this tissue. This study therefore tested the possibility that adenosine may influence the vascular responses to sympathetic nerve stimulation. Intraarterial infusion of adenosine (5–20 μM in arterial blood) increased the resting vascular conductance (from 0.048 ± 0.007 to 0.095 ± 0.013 ml ± min^-1100 g^-1± mmHg^-1) and the percental reduction in vascular conductance due to sympathetic nerve stimulation (4 Hz) by 34 per cent (p<0.05) and to i. a.noradrenaline by 27 per cent (p<0.05). The vasodilator response due to nerve stimulation after α-blockade was reduced by adenosine. Dipyridamole (0.5–1.5 μM) + EHNA (3–10 μM), which increases plasma adenosine levels, had similar effects to adenosine, while theophylline (30–80 μM) decreased the vasoconstrictor response. The vasoconstrictor escape was enhanced by EHNA alone and in combination with dipyridamole, but was reduced by theophylline. On the other hand, the poststimulatory hyperemia was unaffected by adenosine, dipyridamole and EHNA, and theophylline. The results show that adenosine does not reduce the magnitude of the initial vasoconstrictor response in proportion to the increase in resting blood flow. The autoregulatory escape in adipose tissue during nerve stimulation appears to be mediated both by adenosine and by noradrenaline acting on β-adrenoceptors. Poststimulatory hyperemia does not seem to be greatly influenced by exogenous or endogenous adenosine     

Metabolic effects of blood flow restriction in adipose tissue

The metabolic effects of blood flow restriction were studied in isolated blood-perfused canine subcutaneous adipose tissue. Blood flow restriction (on the average to 20 per cent of control flow) was caused by either mechanical clamping of the arterial inflow or by i.a. injections of methoxamine or angiotensin. Glucose uptake in the adipose tissue was reduced during blood flow restriction. This was partially compensated for by a period of increased glucose uptake following restoration of flow. Blood flow restriction also caused an increase in the venous lactate/pyruvate ratio. The basal lipolytic rate was decreased during blood flow restriction. Lipolysis induced by brief (5 min) sympathetic nerve stimulation (4 Hz) was not inhibited by blood flow restriction as the total amount of glycerol released from the tissue was unaffected. The outflow rate was reduced during blood flow restriction, but glycerol trapped within the tissue was apparently not reutilized by the fat cells as it was released upon flow restoration. FFA outflow following nerve stimulation was, however, inhibited suggesting increased reutilization of FFA within the tissue. This increased reutiliza-tion may ultimately be caused by the observed change in red./ox.-balance and/or by the limited carrier capacity (albumin) available during blood flow restriction. Three main conclusions may be drawn from the present results. Firstly, plasma levels of glycerol and FFA do not necessarily reflect adipose tissue lipolysis at a given moment. Secondly, the decreased adipose tissue blood flow seems to be a major cause of the lowered FFA-levels during hemorrhage. Thirdly, in contrast to hemorrhage, even severe reduction of adipose tissue blood flow is insufficient to cause irreversible ischemic damage.     

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.     

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.     

Effects of Prostaglandin E1 in Canine Subcutaneous Adipose Tissue in Situ1

The effect of PGE₁ on the uptake of glucose and the release of FFA and glycerol before and after sympathetic nerve stimulation (4 cps) was investigated in perfused canine subcutaneous adipose tissue in situ. Glucose uptake was significantly increased by PGE₁ at all concentrations used (5 times 10^-10 to 7 times 10^-7 M in blood). The effect of PGE₁ on the release of FFA and glycerol in unstimulated adipose tissue was inconsistent. Increases as well as decreases were observed. Lipolysis, as measured by glycerol release, induced by nerve stimulation was inhibited dose-dependently. A 50 per cent inhibition was produced by approximately 1.2 times 10^-7 M PGE₁. Stimulated FFA release was also inhibited but there was no clear dose-response relationship. It is concluded that PGE₁ has similar effects in canine subcutaneous adipose tissue with an intact blood supply as are known to be produced in vitro.     

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.     

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 × 10^-5 cells (pH 6.6). The maximal glycerol production was reduced from 1 300 to 900 nMol × 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.     

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.     

Changes in ATP and Cyclic Nucleotide Levels during Sympathetic Nerve Stimulation in Canine Subcutaneous Adipose Tissue in situ

Subcutaneous adipose tissue in fed, female dogs was isolated. Biopsies of the tissue (30–150 mg) were taken and rapidly frozen in liquid nitrogen before, during and after nerve stimulation (3–4 Hz). In unstimulated adipose tissue the levels of ATP¹ were 74 ± 7 nmol/g, of cyclic AMP 90 ± 12 pmol/g and of cyclic GMP 18 ± 3 pmol/g (mean + S.E.). During sympathetic nerve stimulation the levels of ATP and cyclic GMP fell by 30 and 50% respectively (p < 0.01), while the cyclic AMP content increased by 50 % (p < 0.05). After nerve stimulation there was a marked increase in glycerol release, and the levels of all three nucleotides returned to control. The fall in ATP during nerve stimulation was essentially eliminated by prior adrenergic a-receptor blockade. It is concluded that 1) sympathetic nerve stimulation induces a rapid, reversible fall in tissue ATP content, which may be related to hypoxia secondary to the vasoconstriction, and 2) lipolytic responses to sympathetic nerve stimulation in vivo are preceeded by small increases in the tissue cyclic AMP level, and a 3-fold increase in the cyclic AMP/cyclic GMP ratio.     

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.     

Fate of 3H-Noradrenaline in Canine Subcutaneous Adipose Tissue1

Canine subcutaneous adipose tissue was isolated and perfused with defibrinated blood at a constant rate. Infused ³H-noradrenaline was taken up by the tissue and released spontaneously into blood. Following a washout period of 40 min or more, plasma samples were withdrawn. Radioactive compounds in venous plasma were separated by chromatography on alumina and Dowex. About 30 per cent of the venous radioactivity was identified as unchanged noradrenaline, about 7 per cent as normetanephrine and 14 per cent as deaminated catechols: deaminated O-methylated metabolites accounted for about 45 per cent. This indicates the presence in adipose tissue of both monoamineoxidase and catechol-O-methyl-transferase. Upon stimulation of sympathetic nerves to adipose tissue peripheral resistance increased, the ³H-presence in adipose tissue of both monoamine oxidase and catechol-O-methyl-transferase. Upon cessation of the stimulation the peripheral resistance decreased and the outflow of noradrenaline metabolites increased above control values. After dihydroergotamine, nerve stimulation induced a decreased peripheral resistance, an increase of ³H-noradrenaline outflow and no change or an increase in the outflow of noradrenaline metabolites. Totally more radioactivity was released upon nerve stimulation after dihydroergotamine. The changes seen are interpreted to be associated with vascular reactions in adipose tissue.     

Olfactory stimulation with scent of grapefruit oil affects autonomic nerves, lipolysis and appetite in rats

In a previous study, we found that olfactory stimulation with scent of grapefruit oil (SGFO) excites the sympathetic nerve innervating the white adipose tissue in rats. Here we further examined the effects of SGFO in rats and observed that olfactory stimulation with SGFO excited the sympathetic nerves innervating the brown adipose tissue and adrenal gland and inhibited the parasympathetic gastric nerve. Local anesthesia of the nasal mucosa with xylocaine or anosmic treatment using ZnSO₄ eliminated the autonomic changes caused by SGFO. Moreover, stimulation with SGFO elevated the plasma glycerol level, and treatment with either ZnSO₄ or an intraperitoneal injection of diphenhydramine, a histamine H1 receptor-antagonist, abolished the glycerol elevation by SGFO. Furthermore, a 15-min exposure to SGFO three times a week reduced food intake and body weight. Finally, limonene, a component of grapefruit oil, induced reponses similar to those caused by SGFO, and diphenhydramine eliminated the glycerol response to limonene. Thus, the scent of grapefruit oil, and particularly its primary component limonene, affects autonomic nerves, enhances lipolysis through a histaminergic response, and reduces appetite and body weight.     

Some Characteristics of Lipolysis in Rabbit Adipose Tissue. Effects of Noradrenaline,ACTH, Theophylline and Prostaglandin El

Perirenal adipose tissue from rabbits of different strains was incubated in vitro and the glycerol release determined to evaluate the lipolysis. Noradrenaline was found to stimulate lipolysis, but to a lower degree than ACTH. From one strain of rabbits it was apparent that lighter (younger) rabbits were more responsive to noradrenaline than heavier (older) animals, some of which were completely unresponsive to the catecholamine. Theophylline as well as PGE, were ineffective when added alone to the incubation medium. However, theophylline increased the glycerol release induced by noradrenaline and low concentrations of ACTH and PCE, inhibited lipolysis under these conditions. The results suggest that there is a low rate of formation of cyclic AMP in rabbit adipose tissue under basal conditions of incubation while the hormonal stimulations might well operate by means of increasing the accumulation of cyclic AMP.     

Effect of Sympathetic Nerve Stimulation on Net Transvascular Movement of Fluid in Canine Adipose Tissue

Net transvascular movement of fluid has been studied in the isolated, autoperfused subcutaneous adipose tissue of the dog, during and after sympathetic nerve stimulation (1–15 Hz) and during infusion of 50% glucose i.a. Net fluid movement was calculated as the difference between change in tissue volume and change in blood volume. Tissue volume was measured by plethysmography and blood volume by external monitoring of circulating ¹³¹I-albumin. No net fluid movement of statistical significance was found during or after nerve stimulation except during the first minute of stimulation at 15 Hz when a small net absorption (p<0.05) was obtained. In contrast, infusion of glucose at 25–75 mOsm/kg H₂O produced a dose-dependent net absorption lasting several minutes, amounting maximally to 0.30 ml × min^-1× 100 g^-1. The absence of prolonged net absorption in subcutaneous adipose tissue during nerve stimulation as well as the absence of net filtration after stimulation may be explained by an essentially unaltered mean hydrostatic capillary pressure. The results indicate that adipose tissue does not contribute to the fluid homeostasis of the body via sympathetic resetting of the pre-postcapillary resistance ratio. Thus, mobilisation of fluid from the nterstitial space in adipose tissue into the blood does not seem to occur by nerve activity.     

Olfactory stimulation with scent of lavender oil affects autonomic nerves, lipolysis and appetite in rats

In a previous study, we presented evidence that scent of grapefruit oil excites sympathetic nerves innervating white and brown adipose tissues and the adrenal gland, inhibits the vagal nerve innervating the stomach, increases lipolysis and heat production (energy consumption), and reduces appetite and body weight. Here, we examined the effects of olfactory stimulation with scent of lavender oil (SLVO) in rats and observed that in contrast to grapefruit oil, it inhibits the sympathetic nerves innervating the white and brown adipose tissues and adrenal gland and excites the parasympathetic gastric nerve. Local anesthesia of the nasal mucosa with xylocaine or anosmic treatment using ZnSO(4) eliminated the autonomic changes caused by SLVO. Moreover, stimulation with SLVO lowered the plasma glycerol level, and treatment with either ZnSO(4) or an intracranial injection of thioperamide, a histamine H3 receptor-antagonist, abolished SLVO-mediated glycerol decline. Furthermore, a 15-min daily exposure to SLVO increased food intake and body weight. Finally, linalool, a component of lavender oil, induced responses similar to those caused by SLVO, and the glycerol response to linalool was eliminated by thioperamide. Thus, scent of lavender oil and its active component, linalool, affect autonomic nerves, suppress lipolysis through a histaminergic response, and enhance appetite and body weight.     

Effect of reflex stimuli on vascular resistance and glycerol release in in vivo dog subcutaneous adipose tissue

Summary Although direct autonomic nerve stimulation and infusion of catecholamine has been shown to result in substantial amounts of lipolysis in dog subcutaneous adipose tissue, there is no evidence to indicate that reflex autonomic stimulation will result in qualitatively and quantitatively similar changes. The present studies were, performed to evaluate the effects of reflex autonomic stimulation on vascular resistance and glycerol release in isolated, innervated and blood-perfused subcutaneous fat pad. Autonomic nerve stimulation at physiological frequencies was performed and resulted in release of glycerol that was compatible with previously reported data. Reflex stimulation by moderate and severe hypoxemia did not result in a significant glycerol release, but a maximal reflex stimulus (ventricular fibrillation) did. Since the majority of these reflex stimuli resulted in large changes in vascular resistance, it would appear that reflex hemodynamic changes can occur in these preparations without concommitant changes in glycerol release. Alpha blockade of the vasoconstriction resulted in the appearance of rising glycerol output suggesting that vasoconstriction prevents lipolysis.Supported by: American Heart Association Grant 72-615 and NIH, Medical Cardiology Training Grant HL05635 (Drs. Croke and Longo) and by USPHS Career Developement Award I KOY HF46346 (Dr. Skinner).     

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.     

The Effect of Lactate in Canine Subcutaneous Adipose Tissue in Situ1

Fredholm , B. B. The effect of lactate in canine subcutaneous adipose tissue in situ. Acta physiol. scand. 1971. 81. 110–123. Na-L(+)-lactate and Na-pyruvate were administered by intraarterial infusion in canine subcutaneous adipose tissue, perfused with the dogs own blood either at a constant rate from a reservoir or by autoperfusion. The glucose uptake was found to be dependent upon the arterial glucose concentration. Similarly the uptake of lactate and pyruvate increased with increasing arterial concentrations, the latter more rapidly than the former. Infusion of Na-L(+)-lactate below 5 mM and Na-D(—)-lactate (10–11 mM) had no effect on the release of FFA and glycerol upon nerve stimulation (4 cps for 5 to 10 min). On the other hand Na-L(+)-lactate above 10 mM caused a 70 per cent inhibition of the release of FFA without significantly affecting the glycerol release. Na-pyruvate (5 mM) decreased the glycerol output significantly, but increased the FFA release. Neither of the anions had any significant effect on the glucose uptake. Na-lactate was not vasoactive, whereas Na-pyruvate was slightly vasodilator. It is concluded that lactate in concentrations occurring a.g. during muscular exercise and shock is capable of significantly depressing the rate of FFA release upon nerve stimulation by increasing the rate of re-esterification. The finding that lactate and pyruvate had opposite effects on esterification indicates a role of the cytoplasmatic NADH/NAD ratio in determining the rate of esterification.