Acute or chronic exercise alters angiotensin II-induced contraction of rat aorta

Chronic exercise substantially shifted the dose-response curve for angiotensin II (ANG II)-induced contractions to the right with increases in the EC50 value in both endothelium-intact and endothelium-denuded aortae. An acute endurance exercise also caused a 3-fold increase in the EC50 value in both endothelium-intact and endothelium-denuded aortae from sedentary control rats. Whereas, no substantial increase in the EC50 value was observed in trained rats after an acute endurance exercise. Thus, chronic exercise attenuates ANG II receptor-mediated contraction of rat aortae. An acute exercise also caused the reduced responses to ANG II in sedentary control rats but not in chronically exercise-trained rats.

Ca2+ and lipolysis in adipocytes from exercise-trained rats

The effects of Ca2+ on lipolysis and protein kinase activity in adipocytes from exercise-trained rats were investigated. Chronic exercise significantly increased lipolytic responses to norepinephrine and dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP). The inhibitory effects of N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7), a calumodulin inhibitor, on norepinephrine- and dibutyryl cAMP-stimulated lipolysis were significantly greater in trained than in sedentary rats. Training did not alter cAMP-dependent protein kinase activity. However, the inhibitory effect of W-7 on cAMP-dependent protein kinase activity was much greater in trained than in sedentary rats. The basal intracellular free Ca2+ concentration ([Ca2+]i) was significantly higher in trained than in sedentary rats. The rapid and transient increases in [Ca2+]i due to adrenocorticotropic hormone and phenylephrine from basal levels were significantly lower in trained than in sedentary rats. However, the higher basal [Ca2+]i level in trained rats led to increases in sustained [Ca2+]i levels after stimulation. We concluded that in trained rats the regulation of protein kinase activity by cAMP depends to a greater degree on Ca(2+)-calmodulin complex than it does in sedentary rats and that training alters adipocyte intracellular Ca2+ homeostasis, including [Ca2+]i responsiveness to hormones.

Increase in cytosolic free Ca2+ in corticotropin-stimulated white adipocytes

The mechanism of the adrenal corticotropin hormone (ACTH)-stimulated increase in cytosolic free Ca2+ concentration ([Ca2+]i) was investigated in rat white adipocytes. ACTH at concentrations > 10 mU/ml caused a rapid and transient increase in [Ca2+]i followed by a small but sustained elevation of [Ca2+]i. A similar phenomenon was also induced by alpha-adrenergic or synthetic ACTH stimulation. The effect of norepinephrine (NE) plus ACTH on [Ca2+]i was nearly additive. Pertussis toxin completely blocked the ability of ACTH or NE to increase [Ca2+]i. NE but not ACTH caused a significant increase in inositol 1,4,5-trisphosphate levels. ACTH caused a rapid and transient accumulation of [3H]arachidonic acid (AA) and a marked loss of [3H]AA from phosphatidylinositol (PI) and phosphatidylcholine (PC) 10 s after stimulation. Neither a lipoxygenase inhibitor nor a dual inhibitor of cyclooxygenase and lipoxygenase blocked the increases in [Ca2+]i and the accumulation of [3H]AA in response to ACTH. On the other hand, either pertussis toxin or phospholipase A2 inhibitor drastically blocked both parameters in response to ACTH. These results indicate that ACTH stimulates AA release from PC and PI via the activation of phospholipase A2 coupled with pertussis toxin-sensitive GTP-binding protein(s), which leads to an increase in [Ca2+]i in rat white adipocytes.

Lack of the stimulatory effect of guanine nucleotide on diacylglycerol generation in permeabilized adipocytes from diabetic rats

Insulin caused an 8- or a 3-fold increase in lipogenesis in control rats (C) or diabetic rats (DM), respectively. Following insulin treatment for DM, insulin resistance was clearly reversed. Phospholipase C (PLC) caused a 4-fold increase in lipogenesis in C, but not in DM. Insulin treatment partially restored PLC-induced lipogenesis. Insulin or PLC increased protein kinase C (PKC) activity in the membrane fraction in C, but not in DM. Insulin treatment partially restored insulin- or PLC-stimulated PKC activity. 5'-Guanylylimidodiphosphate (Gpp(NH)p) exerted a stimulatory effect on diacylglycerol (DAG) generation in permeabilized adipocytes from C, but not in DM. Insulin treatment partially restored the stimulatory effect of Gpp(NH)p. These findings suggest that a particular G protein(s) is involved in the regulation of DAG generation in adipocytes, and that diabetes leads to a functional or quantitative abnormality in G protein and G protein-PLC. Insulin therapy partially restored G protein-PLC dependent glucose uptake.

Mechanism of isoprenaline-stimulated diacylglycerol formation in rat parotid acinar cells

The kinetics and mechanism of sn-1,2-diacylglycerol (DAG) formation induced by isoprenaline were studied in rat parotid acinar cells. DAG accumulation induced by 100 microM isoprenaline reached its maximum at 1 min, rapidly decreased (about 50%) at 5 min and then remained constant for 30 min. DAG accumulation 1 min after isoprenaline treatment was dose-dependent. Either propranolol or phentolamine inhibited isoprenaline-stimulated DAG accumulation in a dose-dependent manner. Addition of a vasoactive intestinal polypeptide, forskolin, or dibutyryl cyclic AMP had no effect on DAG accumulation. Isoprenaline did not cause the release of [3H]choline or [3H]ethanolamine metabolites into the medium. Based on the kinetics of DAG formation and [32P]phosphoinositide breakdown, we conclude that isoprenaline-induced DAG formation was mainly related to the hydrolysis of [32P]phosphatidylinositol 4,5-bisphosphate ([32P]PIP2). These results suggest that the effect of isoprenaline on DAG formation is mediated by alpha 1-adrenoceptor activation, that it is not related to the increase in cyclic AMP, and that it is closely related to PIP2 hydrolysis.

Effect of insulin on adipocyte lipolysis in exercise-trained rats

The effect of exercise training on the antilipolytic action of insulin was studied in rat adipocytes. Exercise training enhanced lipolysis induced by norepinephrine. Insulin dose dependently inhibited norepinephrine- (1 microM) stimulated lipolysis in both groups. Its inhibition rate was significantly greater in the trained than in the control group. Thus, exercise training enhanced the antilipolytic action of insulin. In the control group, insulin (1,000 microU/ml) reduced the displacement rate of [3H]CGP-12177 binding to adipocytes by low concentrations of (-)-norepinephrine. The slope factor without insulin was 0.76, whereas that with insulin was 0.95. In the trained group, insulin did not affect the competition binding of (-)-norepinephrine for [3H]CGP-12177. The displacement rate of [3H]CGP-12177 binding from adipocytes by low concentrations of (-)-norepinephrine was significantly greater in the trained than in the control group. The number of surface beta-adrenergic receptors per adipocyte was smaller in the trained than in the control group. Cilostamide, which blocks the antilipolytic action of insulin, restored lipolysis in both groups. The recovery rate was significantly greater in the trained than in the control group. These findings suggest that the enhanced antilipolytic action by insulin in the trained group occurs at a site distal to the binding of norepinephrine to beta-adrenergic receptors and that it is due to the increased activity of particulate low-Michaelis constant phosphodiesterase.

Intralysosomal pH and release of lysosomal enzymes in the rat liver after exhaustive exercise

The mechanism underlying exhaustive exercise-induced release of lysosomal enzymes was studied in the rat liver. Exhaustive exercise resulted in the release of beta-glucuronidase and cathepsin D, but not beta-glucosidase and acid phosphatase, into the blood and cytosol, suggesting that the release of lysosomal enzymes is not due to disruption of lysosomal membranes. The intralysosomal pH of the liver, which was approximately 5.5 at the resting level, rose significantly after exhaustive exercise to pH 6.3. In vitro, beta-glucuronidase and cathepsin D were released at an intralysosomal pH exceeding 6.2. In contrast, beta-glucosidase and acid phosphatase were not released. The elevation of intralysosomal pH reduced the aggregation of beta-glucuronidase and cathepsin D. The rate of ammonia accumulation increased markedly in the lysosome-enriched subcellular fraction after exercise. There was a positive relationship between the rate of ammonia accumulation and the elevation of intralysosomal pH in vitro. Lysosomes isolated after exhaustive exercise showed significantly increased osmotic fragility. Our findings suggest that, during exhaustive exercise, the accumulation of ammonia in lysosomes leads to the elevation of intralysosomal pH, resulting in the reduced aggregation of certain lysosomal enzymes. Thus, less aggregated lysosomal enzymes may be released into the cytosol through the lysosomal membrane, the permeability of which has been increased.

Effect of running training on uncoupling protein mRNA expression in rat brown adipose tissue

The effect was investigated of endurance training on the expression of uncoupling protein (UCP) mRNA in brown adipose tissue (BAT) of rats. The exercised rats were trained on a rodent treadmill for 5 days per week and a total of 9 weeks. After the training programme, a marked decrease in BAT mass was found in terms of weight or weight per unit body weight; there was a corresponding decrease in DNA content and a downward trend in RNA and glycogen levels. The UCP mRNA was present at a markedly decreased level in BAT of trained animals. In consideration of the reduced levels of mRNAs for hormone-sensitive lipase and acyl-CoA synthetase, the brown adipose tissue investigated appeared to be in a relatively atrophied and thermogenically quiescent state.

Recovery of beta-receptors and adenylate cyclase from desensitization induced by short term heat exposure in rat parotid glands

1. The recovery of rat parotid beta-adrenergic receptors (beta-AR) and adenylate cyclase (AC) from heat (33 degrees C)-induced desensitization was studied. 2. Down-regulated cell surface beta-AR and AC activity in response to isoprenaline (IPR) returned to the control level 120 hr after the termination of heat exposure. 3. However, beta-AR in parotid crude membranes increased over the control level for 48-120 hr. 4. Coupling between beta-AR and G protein(s) was attenuated at 120 hr. 5. These data suggest that beta-AR on the cell surface, but not those internalized, can transduce biological responses.

Effect of endurance training on angiogenic activity in skeletal muscles

The effect of endurance training on angiogenic activity in skeletal muscle was investigated using cell culture. The exercised rats were trained on a rodent treadmill, 5 days a week for 9 weeks. After the training program, a significant increase (7.8%) in mass was found in soleus muscle (MS), although we noted no apparent increase in gastrocnemius muscle and extensor digitorum longus muscle. The extracts from all the muscles (especially from the MS) of trained rats considerably increased the capillary growth in an in vitro angiogenesis model, in which microvascular fragments and myofibroblastic (Mf) cells isolated from lipid tissues were grown in co-culture. In addition, the extract from the MS of trained rats increased the DNA synthesis and growth of bovine capillary endothelial (BCE) cells, although the extract did not stimulate the growth of Mf cells. Moreover, the extract from the MS of trained rats notably enhanced the activity of plasminogen activator in the conditioned medium of BCE cells compared with that of sedentary rats. On the other hand, extracts from the MS of both sedentary and trained rats increased the synthesis of collagen by Mf cells and metalloproteinase activity in the conditioned medium of BCE cells to the same degree. These results suggest that endurance training increases the angiogenic activity in skeletal muscles.

Phorbol ester alters carbachol-stimulated diacylglycerol formation in parotid acinar cells through the hydrolysis of phosphoinositides and phosphatidylcholine

Incubation of rat parotid acinar cells with phorbol 12,13-dibutyrate (PDBu) resulted in inhibition of carbachol-stimulated formation of sn-1,2-diacylglycerol (DAG). PDBu pretreatment inhibited carbachol-induced turnover of phosphoinositides; this inhibition was indicated by phosphatidylinositol 4,5-bisphosphate breakdown. This pretreatment also attenuated the effect of carbachol on inositol phosphate generation and phosphatidylcholine hydrolysis. These results show that PDBu alters carbachol-stimulated DAG formation through the hydrolysis of phosphoinositides and phosphatidylcholine.

Ca2+ ionophore and phorbol ester stimulate diacylglycerol formation and phosphatidylcholine hydrolysis in rat parotid acinar cells

We investigated the effects of A23187 and phorbol 12,13-dibutyrate (PDBu) on sn-1,2-diacylglycerol (DAG) accumulation and phosphatidylcholine (PC) hydrolysis in rat parotid acinar cells. Both A23187 and PDBu, in concentration ranges of 0.001-0.1 microM, stimulated DAG accumulation and PC hydrolysis in a time- and concentration-dependent manner. Treatment with A23187 and PDBu stimulated the release of [3H]choline and [3H]phosphocholine into the medium, indicating [3H]PC hydrolysis is due to the activation of phospholipases C and D; however, [3H]phosphatidylethanolamine hydrolysis was not indicated. These releases were unaffected by the addition of glucose 6-phosphate, a phosphatase inhibitor. Staurosporine, a protein kinase C inhibitor, significantly inhibited the DAG accumulation and the PC hydrolysis stimulated by these agents. Combinations of A23187 and PDBu potentiated the stimulatory effect which each of these agents alone had on DAG accumulation and PC hydrolysis. This mode of action was additive but not synergistic. These results suggest that DAG accumulation induced by A23187 and PDBu is related to the PC hydrolysis mediated via the activation of phospholipases C and D, and that it is not related to phosphatidylethanolamine hydrolysis.

Ca2+ potentiates corticotropin-induced, but not isoproterenol-induced, [3H]guanosine diphosphate release in rat adipocyte membranes

EGTA abolished corticotropin (ACTH)-stimulated adenylate cyclase in rat adipocyte membranes. In contrast, the potency of guanosine triphosphate (GTP) stimulation of adenylate cyclase activated with ACTH was greater in the presence of Ca2+ (1 mmol/L). EGTA (1 mmol/L) powerfully inhibited ACTH-stimulated [3H]guanosine diphosphate (GDP) release from membranes prelabeled with [3H]GTP in the presence of isoproterenol (ISO) or ACTH, whereas Ca2+ significantly increased it. In contrast, neither EGTA nor Ca2+ affected ISO-stimulated [3H]GDP release. These data clearly show that Ca2+ is necessary for the binding of ACTH to its receptor, and that Ca2+ stimulates the interaction of the ACTH-occupied receptor with GTP-binding proteins.

Mechanism of carbachol-stimulated diacylglycerol formation in rat parotid acinar cells

We studied the relationship between phosphoinositide hydrolysis, phosphatidylcholine hydrolysis, and sn-1,2-diacylglycerol (DAG) formation in response to carbachol stimulation in rat parotid acinar cells. Previously, we demonstrated that DAG formation stimulated with 1 microM carbachol was biphasic: the first peak occurred at 5 min and the second one at 20 min. It was also demonstrated that the second peak was regulated in part by a calmodulin/protein kinase C-dependent mechanism. Based on the kinetic analysis of DAG formation and [32P]phosphoinositide breakdown, the first peak of carbachol (1 microM)-stimulated DAG accumulation was found to be related to the breakdown of [32P]phosphatidylinositol 4-monophosphate ([32P]PIP) and [32P]phosphatidylinositol 4,5-bisphosphate ([32P]PIP2). The second peak was found to be related to [32P]PIP2 breakdown. Carbachol stimulated the release of [3H]phosphocholine into the medium, indicating that the predominant pathway for phosphatidylcholine hydrolysis was via phospholipase C. Moreover, carbachol stimulated the release of [3H]choline metabolites in a time- and dose-dependent manner. This agonist slightly stimulated the release of [3H]ethanolamine metabolites. A calmodulin/protein kinase C-dependent mechanism was also studied and was found to be involved in carbachol-stimulated phosphatidylcholine hydrolysis; W-7, a calmodulin inhibitor and staurosporine, a protein kinase C inhibitor, inhibited the carbachol (1-microM)-induced release of [3H]choline metabolites at 20 min in a dose-dependent manner, but did not have inhibitory effects at 5 min. These results suggest that the first peak of DAG accumulation induced by carbachol is predominantly associated with the breakdown [32P]PIP and of [32P]PIP2 and that the second peak is predominantly associated with [32P]PIP2 breakdown and phosphatidylcholine hydrolysis.

Substance P-induced diacylglycerol formation in rat parotid acinar cells

The mechanisms underlying the ability of substance P, to stimulate the sn-1,2-diacylglycerol (DAG) formation were studied using rat parotid acinar cells. During a 60 s stimulation, 1 microM substance P caused a rapid rise in DAG accumulation at 5 s, whereas a low (0.1 microM) concentration of agonist did not. During long term stimulation for 30 min, DAG accumulation induced by 1 microM substance P reached near maximal levels at 5 min and remained elevated for at least 20 min. In contrast, DAG formation induced by 0.1 microM substance P exhibited a peak at 5 min, gradually declined and returned to near basal levels at 30 min. Furthermore, DAG accumulation in response to substance P at 5 and 20 min increased in a dose-dependent manner. The breakdown of both [32P]phosphatidylinositol 4-monophosphate ([32P]PIP) and [32P]phosphatidylinositol 4,5-bisphosphate ([32P]PIP2) stimulated by 1 microM substance P significantly increased from 5 to 20 min and returned to basal levels by 30 min; however, the breakdown of [32P]PIP2 was greater than that of [32P]PIP. At a low concentration of substance P, [32P]PIP2 breakdown reached maximal levels at 5 min followed by a progressive decrease and returned to basal levels at 30 min, whereas the breakdown of [32P]PIP reached maximal levels at 5 min and returned to near basal levels at 10 min. Both concentrations of substance P caused some [32P]phosphatidylinositol breakdown at 5 min. Changes in [3H]inositol trisphosphate induced by substance P were similar to those in [32P]PIP2. In addition, substance P (1 microM) did not stimulate the release of [3H]choline or [3H]ethanolamine metabolites into the medium. Substance P-induced DAG formation was not inhibited by staurosporine, a protein kinase C inhibitor. These results suggest that DAG formation caused by substance P is closely associated with the hydrolysis of phosphatidylinositides but not that of phosphatidylcholine or phosphatidylethanolamine, and is not regulated by protein kinase C-dependent mechanism(s).

Protein kinase C-dependent diacylglycerol formation is mediated via Ca2+/calmodulin in parotid cells

The kinetics of carbachol-induced sn-1,2-diacylglycerol (DAG) formation and the underlying mechanism(s) involved in parotid acinar cells were investigated. Supramaximal concentrations of carbachol for amylase secretion (10 microM) caused a transient rise in DAG levels at 10 s. In contrast, this rapid rise was not elicited by 1 microM carbachol, which is the maximally effective concentration for amylase secretion. Carbachol (10 microM) also increased DAG levels linearly up to 20 min, which were sustained for up to a further 10 min. DAG formation stimulated by 1 microM carbachol was biphasic; the first peak was observed after 5 min and the second after 20 min. DAG formation induced by 0.01-0.1 microM carbachol was concentration-dependent and monophasic, peaking at 5 min. The second peak evoked by carbachol was partly inhibited by Ca2+ deprivation from the extracellular space, whereas the first peak was not. Similar results were obtained in experiments using Ca2+ antagonists such as verapamil and LaCl3. The protein kinase C inhibitors, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) and staurosporine, and a calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), significantly inhibited the second DAG peak produced by 1 microM carbachol, but did not alter the first peak. The degree of inhibition of the second peak by these antagonists was comparable. Furthermore, the inhibitory effect of staurosporine and W-7 was concentration-dependent. The A23187-induced accumulation of DAG also was abolished by both staurosporine and W-7. These data indicate that a protein kinase C-dependent mechanism(s) is involved in mediating the second DAG accumulation peak induced by 1 microM carbachol and is mainly regulated by the Ca(2+)-calmodulin complex.

Enhanced coupling of adenylate cyclase to lipolysis in permeabilized adipocytes from trained rats

Digitonin-permeabilized adipocytes were used to study the coupling of adenylate cyclase (AC) to lipolysis in exercise-trained rats. Isoproterenol-(IPR) stimulated lipolysis in permeabilized cells was significantly greater in trained than in control rats. Under essentially identical conditions, the dose-response curve for IPR stimulation of AC activity in the absence of 3-isobutyl-1-methylxanthine was similar in trained and control rats. However, the potency of stimulation by IPR as a percentage of the basal level was greater in trained rats. AC activity and lipolysis in the presence of 3-isobutyl-1-methylxanthine were also significantly greater in trained than in control rats. Least-squares analysis by plotting the log AC vs. lipolysis values showed that the regression coefficient was about three-fold greater in trained than in control rats. The concentration of endogenous adenosine 3',5'-cyclic monophosphate (cAMP) needed to produce a half-maximal lipolytic response was 18.58 and 10.81 pmol.min-1.10(6) cells-1 in control and trained rats, respectively. Thus a positive relationship existed between lipolysis and AC activity, with a tighter coupling in trained rats. Lipolysis in response to exogenous cAMP tended to be greater in trained than in control rats, and the difference was statistically significant for 50 microM and 10 mM cAMP. Our finding support the concept that the major mechanism of enhanced lipolysis in trained rats was an increase in the activity of enzymatic step(s) distal to cAMP.

Diacylglycerol accumulation is involved in the potentiating effect of A23187 on carbachol-stimulated amylase secretion from parotid gland

We studied the role of sn-1, 2-diacylglycerol (DAG) accumulation in the potentiating effect of A23187 on carbachol (CCh)-stimulated amylase secretion from rat parotid acinar cells. A23187 (0.1 microM) linearly increased DAG accumulation with time for at least 30 min. At concentrations higher or lower than 0.1 microM, DAG levels increased for up to 20 min, but declined at 30 min. Dose-response curve for DAG accumulation induced by A23187 was similar to that for amylase secretion. A23187 augmented CCh-stimulated DAG accumulation and amylase secretion. These results suggest that DAG accumulation is involved in the potentiating effect of A23187 on CCh-stimulated amylase secretion.

A protein kinase C-dependent mechanism(s) is involved in atropine-resistant accumulation of diacylglycerol in rat parotid gland

We investigated the atropine-resistant accumulation of sn-1,2-diacylglycerol (DAG) on stimulation of 1 microM carbachol (CCh) in parotid acinar cells. CCh-induced DAG accumulation was biphasic, peaking at 5 and 20 min. Atropine inhibited two peaks in a dose-dependent manner, but the first peak was inhibited much more than the second one. Atropine (10 microM) completely inhibited both DAG accumulation and the breakdown of phosphatidylinositol 4-monophosphate and 4,5-bisphosphate (PIP2) 5 min after stimulation with CCh. In contrast, the breakdown of PIP2 at 20 min was completely inhibited by 10 microM atropine, but DAG accumulation was not. This atropine-resistant component at 20 min is significantly inhibited by staurosporine, a protein kinase C inhibitor. These results suggest that atropine-resistant accumulation of DAG at 20 min derives directly from other lipids rather than phosphoinositides and is regulated by a protein kinase C-dependent mechanism(s).

Regulation by diacylglycerol of calcium-evoked amylase secretion from intact and permeabilized pancreatic acinar cells

The role of diacylglycerol in the mechanism of amylase release was investigated in isolated rat pancreatic acinar cells. Carbachol produced a time-dependent and dose-related increase in diacylglycerol production which paralleled the time course of amylase secretion. The addition of atropine to acinar cells pretreated with 100 microM carbachol produced a lag in the fall in diacylglycerol levels, which was preceded by a prompt fall in cytosolic Ca2+ and amylase secretion. A threshold concentration of ionomycin amplified the modest action of dioctanoylglycerol on amylase secretion. Ca2(+)-evoked amylase release elicited by saponin permeabilized acinar cells was markedly enhanced by dioctanoylglycerol. These collective findings support the hypothesis that diacylglycerol alone is not an adequate messenger to mediate pancreatic amylase release, but does serve to modulate the actions of Ca2+.

Effects of adenosine and pertussis toxin on lipolysis in adipocytes from exercise-trained male rats

The sensitivity and responsiveness of adipocyte lipolysis to adenosine and pertussis toxin were studied in exercise-trained male rats. Exercise training (9 weeks of treadmill running) significantly increased lipolytic response of adipocytes to noradrenaline (NA). Addition of adenosine deaminase (ADA) to reaction mixture effectively enhanced NA-stimulated lipolysis in adipocytes from both conditioned rats. However, under these conditions, the difference due to exercise training was still evident, although the difference was less pronounced. The inhibition curves of the R-site adenosine analogue N6-phenylisopropyladenosine (PIA) against "basal" (lipolysis in the presence of ADA) and NA-stimulated lipolysis were almost comparable between two groups. Only a small (approx. 2-fold) increase in IC50 of adipocyte lipolysis was observed in each inhibition curve in exercise-trained rats. Within 120 min of addition of pertussis toxin to adipocytes from control rats, "basal" lipolysis was significantly increased as compared to "basal" lipolysis in the absence of toxin at the same point. Similarly, pertussis toxin significantly increased "basal" lipolysis in exercise-trained adipocytes. However these were relatively sensitive to pertussis toxin, since significant effect of toxin was seen within 60 min. An addition of NA (0.1 uM) to the medium in the presence of ADA and toxin significantly increased adipocyte lipolysis in both conditioned rats. Again, under these conditions, we observed that the maximal rate of lipolysis of adipocytes from exercise-trained rats was increased as compared to control rats. These results suggest that the decreased input through the inhibitory pathway in lipolytic cascade may be not rate limiting for the amplified lipolytic responsiveness of adipocytes to hormonal stimuli in exercise-trained rats.

Beta-adrenergic receptor adaptation after an acute exercise in rat myocardium

An acute dynamic exercise provokes the translocation of beta-adrenergic receptors (beta-AR) from light vesicle fractions to sarcolemmal membranes in rat myocardium. However, 15 min after an acute exercise the density of beta-AR in both fractions returned to the pre-exercise level. The mean maximal activity of adenylate cyclase in response to isoproterenol roughly paralleled the redistribution of beta-AR. The dose-response curves, however, were substantially shifted to the right with increase in EC50 for isoproterenol stimulation of adenylate cyclase. Thus, the sensitivity of sarcolemmal beta-AR was found to be blunted 15 min afterwards.

An acute exercise-induced translocation of beta-adrenergic receptors in rat myocardium

The effect of acute exercise (treadmill running) on rat myocardium beta-adrenergic receptors (beta-AR) was studied. beta-AR was identified in purified sarcolemmal membrane fractions and light vesicle fractions. In control hearts, the number of beta-AR was 21.25 +/- 2.25 and 20.89 +/- 2.89 fmol/mg protein (mean +/- SE) in sarcolemmal membranes and light vesicles, respectively. Immediately after a single bout of dynamic exercise, about 35% of beta-AR was transferred from light vesicles to sarcolemmal membranes (p less than 0.05); concomitantly, isoproterenol-stimulated adenylate cyclase activity also significantly increased in sarcolemmal membranes (p less than 0.05). These results suggest that acute exercise provokes the translocation of beta-AR from a presumably intracellular site (light vesicles) to functional membrane fractions (sarcolemmal membranes) in rat myocardium.

Some characteristics of the beta-adrenergic system in rat adipocyte membranes after the chronic administrations of isoproterenol

The effects of chronic administrations of isoproterenol (IPR) on adipocyte beta-adrenergic system were investigated. A 21-days in vivo administration of IPR (2.5 mg/kg BW/day) reduced (-)-IPR- and 5'-guanylylimidodiphosphate-stimulated adenylate cyclase activities. Moreover, the number of beta-adrenergic receptors (beta-AR) and (-)-IPR-stimulated [3H]GDP release from adipocyte membranes were significantly depressed in the treated rats compared to controls. These results suggest that the desensitized response of adenylate cyclase to beta-agonists, induced by chronic in vivo administrations of IPR, may result from impaired coupling efficiency between beta-AR and adenylate cyclase with the significant loss of the number of beta-AR and possible change(s) of guanine nucleotide regulatory proteins.