Stress-induced alteration in the lipolytic response to β-adrenoceptor agonists in rat white adipocytes

The influence of angiotensin II and RAAS blockers on lipolytic and glycolytic activity in isolated adipocytes from Wistar, Wistar-Kyoto and Spontaneously Hypertensive Rats

The renin-angiotensin-aldosterone system (RAAS) is related to dysfunctional adipose tissue, but the actions of angiotensin II (AII) in adipocytes remains unclear. This study aimed to investigate the effects of RAAS blockers and AII in lipolysis and glycolysis from isolated adipocytes in Wistar (WIS), Wistar-Kyoto (WKY) and Spontaneously Hypertensive Rats (SHR). Adipocytes from 15-weeks-old WIS, WKY and SHR were incubated with AII (10-17 M to 10-6 M) and noradrenaline (NOR - 10-10 M to 10-4 M) in presence or not of antagonists (Losartan Potassium 10-4 M, PD 123319 5.6 nM or co-incubation). Glycerol and lactate production in WIS and WKY were not affected by the RAAS blockade. SHR glycerol was attenuated by the blockers but lactate was not affected. NOR induced increase in glycerol from 10-7 M for all strains. Normotensive rats are not affected by blockers but decreased lipolytic activity ins SHR. The SHR hypolipodistrophy cannot be related to any disturbance in lipolytic or glycolytic upstream pathways.

Ultrasound associated with caffeine increases basal and beta-adrenoceptor response in adipocytes isolated from subcutaneous adipose tissue in pigs

BACKGROUND

The topical use of caffeine has been indicated for the lipodystrophies treatment as it promotes increased lipolysis. Ultrasound (US) is often used in cutaneous diseases, esthetic conditions, and as a skin permeation enhancer.

OBJECTIVE

We investigate the lipolytic response of adipocytes isolated from subcutaneous adipose pigs tissue subjected to treatment with topical application of phonophoresis associated with caffeine.

METHOD

We treated dorsal regions of pigs (Landrace × Large White, 35 days, 15 kg, n = 6) daily for 15 days with gel, gel + US [3 MHz, continuous, 0.2 Wcm(2), 1 min/cm(2), in total 2 min], gel + caffeine (5%w/w), and gel + caffeine + US. We used a fifth untreated region as control. Twenty-four hours after the last application, we isolated the adipocytes of each treated area and quantified the basal and stimulated lipolytic responses to isoprenaline. The results, in μmol glycerol/10(6)cells/60 min, were analyzed with analysis of variance or ANOVA followed by Newman-Keuls test. The value of p < 0.05 was indicative of statistical difference.

RESULTS

Only the adipocytes isolated from the area treated with caffeine + US showed increased basal lipolysis (0.76 ± 0.26; p = 0.0276) and maximal isoprenaline stimulation (0.38 ± 0.15, p = 0.0029) compared with the other areas.

CONCLUSION

The results demonstrate that increased lipolysis of caffeine + US is due to an increase in basal and beta-adrenoceptor response by caffeine, and caffeine's effect is local, avoiding unwanted effects.

Adrenoceptors and adaptive mechanisms in the heart during stress

Several cardiovascular disorders have been related to alterations in beta-adrenoceptor (beta-AR) signaling at or beyond the receptor level. During the stress reaction, the sympathetic-adrenal medullary system and the hypothalamus-pituitary-adrenal cortex axis are activated, causing beta-AR overstimulation and remodeling of the beta(1)/beta(2)/beta(3)-AR ratio in cardiomyocytes. In a model of foot-shock stress, we described decreased beta(1)-AR signaling occurring simultaneously with increased beta(2)-AR signaling, whereas the response to the nonconventional agonist, CGP12177, was not altered. These alterations may play an adaptive role to the increased sympathetic drive to the heart, protecting the cardiac tissue from the cardiotoxic effects mediated by beta(1)-ARs overstimulation without altering cardiac output, since this would be sustained by the beta(2)-AR, which would also protect myocytes from apoptosis. Moreover, the selective enhancement of the beta(2)-AR population might help to diminish the risk of overstimulation since this adrenoceptor subtype couples to both, stimulatory G (Gs) and inhibitory G (Gi) proteins. On the other hand, in the model of neurogenic hypertension, the decrease in beta(1)-AR-mediated response is not followed by increase in the beta(2)-AR-mediated response. However, the response to CGP12177, which was desensitized 48 h after the surgery, was normalized 7 days after that, when beta(1)-AR were downregulated. Therefore, both experimental models provided evidence that the classical isoform of beta(1)-AR and the recently described low-affinity isoform of beta(1)-AR show independent behavior and provide the heart with adaptive mechanisms to increased sympathetic stimulation during stress.

Mutations in the beta1 adrenergic receptor gene and massive obesity in Japanese

Catecholamines strongly promote lipolysis and thermogenesis, and play a central role in the regulation of body fat content. The beta1 adrenergic receptor (BAR-1) is a major mediator of catecholamine-induced lipolysis and thermogenesis. To explore whether mutations in the BAR-1 gene contribute to morbid obesity in Japanese, we scanned for mutations in the coding sequence of the gene in 50 morbid obese [body mass index (BMI)>==35.0kg/m(2); 99.7th percentile] Japanese subjects. Direct DNA sequencing was performed following polymerase chain reaction (PCR) amplification. Two common polymorphisms, Gly49Arg and Arg389Ser, were detected in these subjects. The frequencies of these polymorphisms, as determined by PCR-restriction fragment length polymorphism (RFLP) analysis, showed no significant difference between 180 severely obese subjects (BMI>==30.0kg/m(2); 97th percentile) and 132 control (BMI<25.0kg/m(2)) subjects. This study represents the first investigations of genetic variations of BAR-1 in relationship to morbid obesity and suggests mutations in the BAR-1 coding sequence is not likely a major cause of morbid obesity at least in Japanese.

Decreased core temperature and increased beta(3)-adrenergic sensitivity in diabetes-prone BB rats

BACKGROUND

Diabetes-prone (DP) congenic DR.lyp/lyp BioBreeding (BB) rats all develop Type 1 diabetes between 50 and 81 days of age, while DR.lyp/+ or DR.+/+ BB rats are diabetes resistant (DR). The DP rats display reduced weight gain prior to developing hyperglycemia, implying that metabolic events may precede diabetes onset. We tested the hypothesis that temperature measurements could serve as a physiological marker for the impending onset of hyperglycemia.

METHODS

Prior to the onset of hyperglycemia, brain, lower back, and intrascapular brown adipose tissue temperatures were analyzed by thermal signature analysis, which measures infrared emission from tissues. A thermocoupled rectal probe measured core temperature. In addition we performed a beta(3)-adrenergic receptor challenge test with the beta(3)-adrenergic receptor agonist BRL37344.

RESULTS

DP rats displayed lower core temperature than DR rats prior to the onset of hyperglycemia. No temperature difference was detected in brain, lower back, or intrascapular brown adipose tissue between DP and DR rats. The beta(3)-adrenergic challenge showed that the rate of temperature increase after administration of BRL37344 was significantly higher (0.005 +/- 0.002 degrees C/min) in DP than in DR rats (P = 0.044).

CONCLUSIONS

These studies reveal that the prediabetic DP rats fail to maintain core temperature and that they display increased sensitivity to heat production induced by a beta(3)-adrenergic receptor agonist. These studies suggest that body temperature as a measure of metabolic dysregulation is altered in the prediabetic DP rat prior to the onset of hyperglycemia.

Stress and cardiac beta adrenoceptors

Most modern theories about stress recognize that although stress is not a disease, it may be the trigger for the majority of diseases when allostatic overload has been generated. During stress, the glucocorticoids and catecholamines play a key role in the regulation of physiological parameters and homeostasis during stress. In the heart, positive chronotropic, inotropic, and lusitropic responses to catecholamines are mediated by various subtypes of adrenergic receptors (beta-ARs), mainly beta1- and beta2-adrenergic receptors. beta-ARs also control cardiomyocyte growth and death, thus contributing to cardiac remodelling. The structural basis of each beta-AR subtype, as well as their signalling pathways, and adaptive responses to stress are discussed. The participation of beta3- and putative beta4-ARs in the control of cardiac function is also discussed, with emphasis on low affinity beta-AR isoforms and the role they play in the response to the catecholamines under stress. The changes in beta-AR signalling under pathogenic conditions as well as under stress are reviewed.

Chronic disruption of body weight but not of stress peptides or receptors in rats exposed to repeated restraint stress

Rats exposed to restraint stress for 3 h on each of 3 days lose weight and do not return to the weight of their non-stressed controls for extended periods of time. Studies described here demonstrate that the initial weight loss is associated with increased energy expenditure and reduced food intake on the days of restraint but that there is no difference between stressed and control rats once stress ends. The failure to compensate for this energy deficit accounts for the sustained reduction in weight which lasts for up to 80 days after the end of restraint. In an additional experiment, in situ hybridization was used to measure mRNA expression of corticotrophin releasing factor (CRF) and CRF receptors in hypothalamic nuclei, of urocortin (UCN) in the Edinger Westphal nucleus and of UCN III in the rostral perifornical area and medial amygdaloidal nucleus. Immediately after the second 3 h bout of restraint stress, there was a significant increase in expression of UCN in the Edinger Westphal nucleus and of CRF-R1 in the paraventricular nucleus of the hypothalamus and a less pronounced decrease in CRF-R2 expression in the ventromedial nucleus of the hypothalamus. There were no differences in expression of stress-related peptides or their receptors 40 days after the end of repeated restraint. These results suggest that the sustained reduction in body weight and increased responsiveness to subsequent stressors in rats that have been exposed to repeated restraint are not associated with prolonged changes in mRNA expression of CRF receptors or their ligands.

Glucocorticoid receptor and Beta-adrenoceptor expression in epididymal adipose tissue from stressed rats

Adipocytes isolated from epididymal adipose tissue of foot-shock stressed rats are supersensitive to isoprenaline and subsensitive to norepinephrine. These alterations are probably mediated by a stress-induced increase in plasma corticosterone levels. We investigated whether foot-shock stress modifies the expression of glucocorticoid receptors (GRs) and beta-adrenergic protein receptors (beta-ARs) in epididymal adipose tissue from rats submitted to one daily foot-shock session on three consecutive days. This stress protocol caused decreases in GR, beta(1)-AR, and beta(3)-AR protein levels, but caused an increase in beta(2)-AR. These results confirm and support previous functional studies. The alterations in protein expression may be modulated by the high corticosterone levels that downregulate the glucocorticoid receptor.

Effect of swimming session duration and repetition on metabolic markers in rats

The aim of this study was to investigate the profile of metabolites in male rats subjected to 50-60 min of swimming on three protocols: group A, a single 50 min swimming session; group B, one session a day for three days (5 min on day 1, 15 min on day 2 and 30 min on day 3); and group C, one session a day for 5 days, with increasing duration from 5 min on day 1, 15, 30, 45 and 60 min on consecutive days. The interval between sessions was 24 h. Measurements were made after the last swimming session. Controls did not swim. The glycogen content of liver and gastrocnemius and soleus muscle was depleted in the three groups that swam, but blood glucose concentration was significantly increased only in group B. Serum lactate concentrations were greater than the controls in groups A and B. There were significant increases in serum free fatty acid concentrations in all groups that swam. The increases in plasma free fatty acids may have resulted from lipolysis stimulated by endogenous catecholamines in groups A and C, since basal lipolysis measured in vitro was unchanged by swimming. The large increase in basal lipolysis in group B may have contributed to the rise in plasma free fatty acids. Adipocytes from rats in groups A and B were supersensitive to epinephrine, whereas those from group C were not. We conclude that the metabolic alterations were less pronounced after the last of five swimming sessions over 5 days than after a single session, even though session duration and the contribution of the physical component were similar. Glucose mobilization, but probably not utilization, was similar in the three groups that swam. The mechanisms of lipid mobilization from adipose tissue differed, depending on the stress paradigm. The metabolic changes in groups A and B indicated that three daily swimming sessions were insufficient to cause adaptation. The results contrast with previous findings for foot-shock stress, which leads to sensitization rather than adaptation in response to repeated stimuli.

Sensitivity to beta-adrenoceptor agonists of adipocytes from rats treated with an aqueous extract of Croton cajucara Benth

Aqueous extracts of Croton cajucara bark are used in folk medicine to treat hepatic and gastrointestinal disorders and as a coadjuvant in weight-loss programs. We examined the effect of treating rats for 15 days with a 5% aqueous extract of C. cajucara on body weight and food intake. The epididymal adipose pads were removed and the lipolytic responses of isolated adipocytes to isoprenaline, noradrenaline (norepinephrine), BRL37344 and adrenaline (epinephrine) were analysed in the absence or presence of metoprolol or ICI118,551. Treated rats had a significantly lower weight gain than control rats, with no difference in food and liquid intake, epididymal fat-pad weight or basal glycerol release. The sensitivity of the lipolytic response to isoprenaline and adrenaline was significantly higher in adipocytes from treated rats. The sensitivity to noradrenaline or BRL37344 was unaltered. Metoprolol shifted the dose-response curves to noradrenaline to the right in adipocytes from control and treated rats; the dose-response curve to isoprenaline in adipocytes from control rats was also shifted to the right. In adipocytes from treated rats, the dose-response curve to isoprenaline was unaltered by metoprolol but was shifted to the right by ICI118,551, a beta(2)-adrenoceptor antagonist. We conclude that in adipocytes from treated rats there is an increase in the lipolytic response to non-selective agonists (isoprenaline and adrenaline) mediated by beta(2)-adrenoceptors, with no alteration in the responses mediated by beta(1)-adrenoceptors (noradrenaline) or beta(3)-adrenoceptors (BRL37344). This effect could increase the role of adrenaline as an endogenous stimulator of lipolysis.

Subsensitivity to insulin in adipocytes from rats submitted to foot-shock stress

We examined the effect of three daily foot-shock stress sessions on glucose homeostasis, insulin secretion by isolated pancreatic islets, insulin sensitivity of white adipocytes, and glycogen stores in the liver and soleus muscle of rats. Stressed rats had plasma glucose (128.3 ± 22.9 mg/dL) and insulin (1.09 ± 0.33 ng/mL) levels higher than the controls (glucose, 73.8 ± 3.5 mg/dL; insulin, 0.53 ± 0.11 ng/mL, ANOVA plus Fisher's test; p < 0.05). After a glucose overload, the plasma glucose, but not insulin, levels remained higher (area under the curve 8.19 ± 1.03 vs. 4.84 ± 1.33 g/dL 30 min and 102.7 ± 12.2 vs. 93.2 ± 16.1 ng/mL 30 min, respectively). Although, the area under the insulin curve was higher in stressed (72.8 ± 9.8 ng/mL) rats than in control rats (34.9 ± 6.9 ng/mL) in the initial 10 min after glucose overload. The insulin release stimulated by glucose in pancreatic islets was not modified after stress. Adipocytes basal lipolysis was higher (stressed, 1.03 ± 0.14; control, 0.69 ± 0.11 µmol of glycerol in 60 min/100 mg of total lipids) but maximal lipolysis stimulated by norepinephrine was not different (stressed, 1.82 ± 0.35; control, 1.46 ± 0.09 µmol of glycerol in 60 min/100 mg of total lipids) after stress. Insulin dose-dependently inhibited the lipolytic response to norepinephrine by up to 35% in adipocytes from control rats but had no effect on adipocytes from stressed rats. The liver glycogen content was unaltered by stress, but was lower in soleus muscle from stressed rats than in control rats (0.45 ± 0.04 vs. 0.35 ± 0.04 mg/100 mg of wet tissue). These results suggest that rats submitted to foot-shock stress develop hyperglycemia along with hyperinsulinemia as a consequence of insulin subsensitivity in adipose tissue, with no alteration in the pancreatic sensitivity to glucose. Foot-shock stress may therefore provide a useful short-term model of insulin subsensitivity.Key words: glucose tolerance test, white adipocytes, lipolysis, pancreatic islets, insulin release, soleus muscle, liver glycogen.

Metabolic markers following beta-adrenoceptor agonist infusion in footshock-stressed rats

Stress hormones can alter metabolic functions in adipose tissue and liver, as well as the sensitivity of rat white adipocytes and rat atrial responses to beta-adrenergic agonists. In this study, we examined the effects of three daily footshock stress sessions on the plasma corticosterone, glucose, glycerol and triacylglycerol levels of fed, conscious male rats, and on the plasma glucose, glycerol and triacylglycerol levels of the same rats following iv infusions of beta-adrenergic agonists (isoproterenol: 0.4 nmol kg-1 min-1, noradrenaline: 5.0 microg kg-1 day-1, and BRL 37344 ([+/-]-[4-(2-[(2-[3-chlorophenyl]-2-hydroxyethyl)amino]propyl)phenoxy]acetic acid), a selective beta3-adrenoceptor agonist: 0.4 nmol kg-1 min-1). Plasma corticosterone levels increased significantly after each stress session, while triacylglycerol levels increased after the first session and glucose increased after the second and third sessions. Glycerol levels were unaltered after stress. These results suggest that repeated footshock stress may induce a metabolic shift from triacylglycerol biosynthesis to glucose release by hepatic tissue, with glycerol serving as one of the substrates in both pathways. Stressed rats were more sensitive to infusion of noradrenaline plus prazosin and to infusion of isoproterenol, with elevated plasma glucose, glycerol and triacylglycerol levels. The higher sensitivity of stressed rats to isoproterenol and noradrenaline was probably related to the permissive effect of plasma corticosterone. Only BRL 37344 increased plasma glycerol levels in stressed rats, probably because beta3-adrenoceptors are not involved in hepatic triacylglycerol synthesis, thus allowing glycerol to accumulate in plasma.