Anesthetic-induced transient hyperglycemia and insulin resistance do not depend on the sympathoadrenal axis.

AIM: Glucose homeostasis is maintained under strict physiological control in which the central nervous system is very important. Ketamine/xylazine mixture induces hyperglycemia, although the mechanism involved is unknown. We aimed to study the role of sympathoadrenal axis on glycemia and insulinemia in adult rats. METHODS: NInety-day-old male Wistar rats were used. Half of the rats underwent removal of the adrenal gland medullae (adrenodemedullation, ADM). After overnight fasting, all rats were given the intravenous glucose tolerance test (ivGTT), which was performed in six groups: awake, ketamine/xylazine (KX) and thiopental (Thiop) anesthetized intact rats, and the same groups of ADM rats. The intraperitoneal insulin tolerance test (1U/kg BW) was performed in an additional animal group to record the rate constant of plasma glucose disappearance (Kitt). Tissue insulin sensitivity was also evaluated by the homeostasis model assessment (HOMA). RESULTS: Ketamine/xylazine increased basal glycemia by 110.6% (P<0.001) in intact rats. In the ADM group, KX rats had a reduction of 36.6% (P<0.05) basal glycemia. Thiop caused a decrease of 70.3% (P<0.05) in basal insulinemia in intact rats. ADM reduced fasting insulin in all groups. Insulin sensitivity was elevated in intact Thiop rats, while insulin resistance was observed in intact KX rats. Both anesthetics induced glucose intolerance during ivGTT in the intact group, but not in ADM rats. Insulin secretion was reduced for both anesthetics in intact and ADM rats. CONCLUSION: Sympathoadrenal axis activity is not involved with the hyperglycemia induced by thiopental or ketamine/xylazine.

An increase in glucose concentration in the lateral ventricles of the brain induces changes in autonomic nervous system activity.

OBJECTIVE: Changes in glucose levels mobilize a neuroendocrine response that prevents or corrects glycemia. The hypothalamus is the main area of the brain that regulates glycemic homeostasis. Metabolic diseases, such as obesity and diabetes, are related to imbalance of this control. The modulation of autonomic nervous system (ANS) activity is mediated by neuronal hypothalamic pathways. In the present work, we investigate whether glucose concentration in the hypothalamic area changes ANS activity. METHODS: Glucose was administered intracerebroventricularly to 90-day-old rats, and samples of blood were collected during brain glucose infusion to measure the blood glucose and insulin levels. The electric activity of the superior vagus nerve and superior sympathetic ganglion was directly registered. RESULTS: Glucose 5·6 mM infused in the hypothalamus induced a 67·6% decrease in blood insulin concentration compared to saline infusion (P<0·01); however, no glycemia changes occurred. During glucose 5·6 mM intracerebroventricular infusion, the firing rate of the vagus nerve was decreased 39% and sympathetic nerve activity was increased 177% compared to saline infusion (P<0·01). DISCUSSION: Glucose injection into the brain in the hypothalamic area modulates glucose homeostasis, which might be mediated by the sensitivity of the hypothalamic area to local changes in glucose concentration. We suggest that gluconeurons in the hypothalamus contribute to the control of glycemia through ANS activity.

Early exposure to a high-fat diet has more drastic consequences on metabolism compared with exposure during adulthood in rats.

The aim of this study was determine whether the introduction of a high-fat diet during the peripubertal phase induces significant changes in body weight control, glucose homeostasis and the parasympathetic tonus compared with the administration of this diet to adult rats. High-fat diet was offered to male Wistar rats at weaning or during adulthood. A group of rats received high-fat diet for 60 days, from weaning to 81-day-old (HF81) or from 60 to 120-day-old (HF120), whereas 2 other groups received a normal-fat diet (i. e., NF81 and NF120). We analyzed adiposity, glucose homeostasis, insulin sensitivity, and vagal nerve activity. High-fat diet increased the accumulation of adipose tissue in all of the rats, but the difference was greater in the rats that were fed the high-fat diet since weaning (p<0.001). The HF rats showed glucose intolerance with high levels of insulin secretion during the glucose tolerance test (p<0.01). Rats that were fed the high-fat diet presented severe insulin resistance, indicated by a low K itt (p<0.01). Interestingly, the HF81 rats exhibited greater insulin resistance compared with the HF120 rats (p<0.05). The recordings of vagus nerve activity showed that the HF rats had higher parasympathetic activity than the NF rats irrespective of age (p<0.01). Our results show that a high-fat diet offered to rats just after weaning or in adulthood both cause impairment of glycemic homeostasis and imbalance in parasympathetic activity. Importantly, the consumption of high-fat diet immediately after weaning has more drastic consequences compared with the consumption of the same diet during adulthood.

Metabolic imprinting by maternal protein malnourishment impairs vagal activity in adult rats.

Protein restriction during lactation has been suggested to diminish parasympathetic activity, whereas sympathetic activity is enhanced in adult rats. The present study analyses whether dysfunction of the autonomic nervous system is involved in the impairment of insulin secretion from perinatally undernourished rats. Male neonates were reared by mothers fed a low- (4%) protein (LP group) or normal- (23%) protein diet (NP group). At 81 days of age, LP rats showed less body mass than NP rats (318 ± 4 g versus 370 ± 5 g) (P < 0.001). Fat tissue accumulation decreased in LP [0.8 ± 0.03 g/100 g body weight (BW)] compared to NP rats (1.1 ± 0.04 g/100 g BW) (P < 0.001). LP were glucose-intolerant as registered by the area under the curve of an i.v. glucose tolerance test (37 ± 3) compared to NP rats (29 ± 2) (P < 0.05); however, LP animals showed fasting normoglycaemia (LP, 5.0 ± 0.1; NP, 4.9 ± 0.03 mm) and hypoinsulinaemia (LP, 0.10 ± 0.02 ng/ml; NP, 0.17 ± 0.02 ng/ml). LP also showed glucose tissue uptake 60% higher than NP rats (P < 0.05). Vagus firing rate from LP was lower (7.1 ± 0.8 spikes/5 s) than that in NP rats (12.3 ± 0.7 spikes/5 s) (P < 0.001); however, there was no difference in sympathetic nervous activity. The cholinergic insulinotrophic effect was lower in pancreatic islets from LP (0.07 ± 0.01 ng/min/islet) than in NP rats (0.3 ± 0.06 ng/min/islet), whereas the levels of adrenaline-mediated inhibition of glucose-induced insulin release were similar. Perinatal protein restriction inhibited the activity of the vagus nerve, thus reducing the insulinotrophic effect of parasympathetic pathways on pancreatic ß-cells, which inhibit insulin secretion.

Swimming exercise at weaning improves glycemic control and inhibits the onset of monosodium L-glutamate-obesity in mice.

Swimming exercises by weaning pups inhibited hypothalamic obesity onset and recovered sympathoadrenal axis activity, but this was not observed when exercise training was applied to young adult mice. However, the mechanisms producing this improved metabolism are still not fully understood. Low-intensity swimming training started at an early age and was undertaken to observe glycemic control in hypothalamic-obese mice produced by neonatal treatment with monosodium l-glutamate (MSG). Whereas MSG and control mice swam for 15 min/day, 3 days a week, from the weaning stage up to 90 days old, sedentary MSG and normal mice did not exercise at all. After 14 h of fasting, animals were killed at 90 days of age. Perigonadal fat accumulation was measured to estimate obesity. Fasting blood glucose and insulin concentrations were also measured. Fresh isolated pancreatic islets were used to test glucose-induced insulin release and total catecholamine from the adrenal glands was measured. Mice were also submitted to intraperitoneal glucose tolerance test. MSG-obese mice showed fasting hyperglycemia, hyperinsulinemia, and glucose intolerance. Severe reduction of adrenal catecholamines content has also been reported. Besides, the inhibition of fat tissue accretion, exercise caused normalization of insulin blood levels and glycemic control. The pancreatic islets of obese mice, with impaired glucose-induced insulin secretion, were recovered after swimming exercises. Adrenal catecholamine content was increased by swimming. Results show that attenuation of MSG-hypothalamic obesity onset is caused, at least in part, by modulation of sympathoadrenal axis activity imposed by early exercise, which may be associated with subsequent glucose metabolism improvement.

Transplantation of pancreatic islets from hypothalamic obese rats corrects hyperglycemia of diabetic rats.

Pancreatic islets isolated from adult obese rats, obtained by neonatal treatment with monosodium L-glutamate (MSG), oversecrete insulin stimulated by glucose concentration. Whereas adult MSG obese rats are hyperinsulinemic, their pancreatic islets still secrete insulin after high glucose demand. This is crucial so that the animals do not become hyperglycemic. Islets from MSG obese rats were implanted in diabetic donor rats so that the capacity of islets in regulating blood glucose concentration could be evaluated. Hyperglycemic (glucose 22 to 34 mmol/L) rats obtained with streptozotocin (STZ) treatment were used as recipients. Islet donors consisted of control adult and MSG obese rats. Only 600 islets were transplanted via the portal vein to diabetic rats. During 4 days after the transplant, fed blood glucose was monitored. After 12 hours of fasting the rats were killed; their blood samples were used to measure glucose and insulin concentration; retroperitoneal fat pads were isolated and weighed to estimate body fat. Transplanted islets from MSG obese rats decreased of fed glucose levels by 34% in diabetic rats (P < .05); however, glucose levels still remained twofold higher than those of intact controls (P < .05). Similar to MSG islets, islets grafts from control rats provoked the same effects in diabetic rats. High fasting blood glucose and low insulin levels of diabetic rats were corrected by islet grafts. Transplantations were able to recover 40% of fat in diabetic rats. The results demonstrated that islets from MSG obese rats may regulate blood glucose concentrations in diabetic rats, and suggesting that their function was not permanently altered by the onset of obesity.

Swim training applied at early age is critical to adrenal medulla catecholamine content and to attenuate monosodium L-glutamate-obesity onset in mice.

Exercise has been recommended as a remedy against a worldwide obesity epidemic; however, the onset of excessive weight gain is not fully understood, nor are the effects of exercise on body weight control. Activity deficits of the sympathetic nervous system, including the sympathoadrenal axis, have been suggested to contribute to high fat accumulation in obesity. In the present work, swim training was used to observe fat accumulation and adrenal catecholamine stocks in hypothalamic-obese mice produced by neonatal treatment with monosodium L-glutamate (MSG). MSG-treated and normal mice swam for 15 min/day, 3 days a week, from weaning up to 90 days old (EXE 21-90); from weaning up to 50 days old (EXE 21-50) and from 60 up to 90 days old (EXE 60-90). Sedentary MSG and normal mice (SED groups) did not exercise at all. Animals were sacrificed at 90 days of age. MSG treatment induced obesity, demonstrated by a 43.08% increase in epididymal fat pad weight; these adult obese mice presented 27.7% less catecholamine stocks in their adrenal glands than untreated mice (p<0.001). Exercise reduced fat accumulation and increased adrenal catecholamine content in EXE 21-90 groups. These effects were more pronounced in MSG-mice than in normal ones. Halting the exercise (EXE 21-50 groups) still changed fat accretion and catecholamine stocks; however, no effects were recorded in the EXE 60-90 groups. We conclude that metabolic changes imposed by early exercise, leading to an attenuation of MSG-hypothalamic obesity onset, are at least in part due to sympathoadrenal activity modulation.

Acute effects of fatty acids on insulin secretion from rat and human islets of Langerhans.

Fatty acids have both stimulatory and inhibitory effects on insulin secretion. Long-term exposure to fatty acids results in impaired insulin secretion whilst acute exposure has generally been found to enhance insulin release. However, there are conflicting data in the literature as to the relative efficacy of various fatty acids and on the glucose dependency of the stimulatory effect. Moreover, there is little information on the responses of human islets in vitro to fatty acids. We have therefore studied the acute effects of a range of fatty acids on insulin secretion from rat and human islets of Langerhans at different glucose concentrations. Fatty acids (0.5 mM) acutely stimulated insulin release from rat islets of Langerhans in static incubations in a glucose-dependent manner. The greatest effect was seen at high glucose concentration (16.7 mM) and little or no response was elicited at 3.3 or 8.7 mM glucose. Long-chain fatty acids (palmitate and stearate) were more effective than medium-chain (octanoate). Saturated fatty acids (palmitate, stearate) were more effective than unsaturated (palmitoleate, linoleate, elaidate). Stimulation of insulin secretion by fatty acids was also studied in perifused rat islets. No effects were observed at 3.3 mM glucose but fatty acids markedly potentiated the effect of 16.7 mM glucose. The combination of fatty acid plus glucose was less effective when islets had been first challenged with glucose alone. The insulin secretory responses to fatty acids of human islets in static incubations were similar to those of rat islets. In order to examine whether the responses to glucose and to fatty acids could be varied independently we used an animal model in which lactating rats are fed a low-protein diet during early lactation. Islets from rats whose mothers had been malnourished during lactation were still able to respond effectively to fatty acids despite a lowered secretory response to glucose. These data emphasise the complex interrelationships between nutrients in the control of insulin release and support the view that fatty acids play an important role in glucose homeostasis during undernutrition.

Insulin secretion and acetylcholinesterase activity in monosodium l-glutamate-induced obese mice.

OBJECTIVE: Pancreatic islets isolated from mice treated neonatally with monosodium L-glutamate (MSG) were used to study insulin secretion. MATERIALS AND METHODS: Total acetylcholinesterase (AchE) activity of tissue extract was measured as a cholinergic activity marker. Obesity recorded in 90-day-old MSG mice (OM) by Lee index reached 366.40 +/- 1.70, compared to control mice (CM) 324.40 +/- 1.10 (p < 0.0001). Glucose 5.6 mM induced insulin secretion of 36 +/- 5 pg/15 min from islets of CM and 86 +/- 13 from OM (p < 0.001). When glucose was raised to 16.7 mM, islets from OM secreted 1,271 +/- 215 and 1,017 +/- 112 pg/30 min to CM. AchE activity of pancreas from OM was 0.64 +/- 0.02 nmol of substrate hydrolyzed/min/mg of tissue and 0.52 +/- 0.01 to CM (p < 0.0001). Liver of obese animals also presented increase of AchE activity. RESULTS: These indicate that OM insulin oversecretion in low glucose may be attributed, at least in part, to an enhancement of parasympathetic tonus.

Undernutrition during early lactation as an alternative model to study the onset of diabetes mellitus type II.

In order to characterize an alternative animal model for the study of diabetes mellitus type II onset, we compared the effects of a diet containing 8% of protein (LPD) and a normal diet containing 25% of protein supplied to the dams during the first 12 days of lactation. We studied in the pups the growth evolution and, when they develop into adults (60 days), the glucose tolerance test (GTT) and the insulin secretion, in response to stimulatory concentrations of glucose. The weight of the two groups were significantly different at 60 days of age (LPD = 179 +/- 19 g; NPD = 186 +/- 18 g). The GTT ten minutes after iv glucose administration showed a significant increase of blood glucose concentration of the LPD group (LPD = 550 +/- 17 mg/dl; NPD = 425 +/- 13 mg/dl, p < 0.001). The insulin secretion, four minutes after stimulation was found reduced in the LPD group (LPD = 1.1 +/- 0.08 muU/islet/min; NPD = 1.85 +/- 0.2 muU/islet/min.). The present study indicates insulin secretory and/or resistance impairment due to early undernutrition. Also, the data taken together suggest that undernutrition during early lactation can be used as an alternative model to study particular characteristics of the onset of diabetes mellitus type II.

Blockade of the 32P phosphate flush of pancreatic beta cells from adult rats who received a low-protein diet during early lactation.

In order to study the effect of nutrition on the onset of disturbances in Wistar rat pancreatic beta cells, we compared the effects of a low protein diet (8% protein) and a normal protein diet (25% protein) supplied to the dams (6 in each group) during the first 12 days of lactation. The parameter evaluated was the beta cells phosphate flush in response to stimulatory concentration of glucose (16.7 mM) of isolated islets of Langerhans from 60-day old pups. Using a collagenase digestion technique, islets were isolated from the pups and the 32P fractional outflow rate (FOR) of the beta cells was used as a metabolic index in both experimental groups (N = 36). We observed that although the weights of the pups of the two groups were not significantly different at 60 days of age (control = 186 +/- 18 g; undernourished during lactation = 179 +/- 19 g), the typical phosphate flush response (FOR = 2.4 +/- 0.4%/min) to a stimulatory glucose concentration (16.7 mM) was abolished in the rats from undernourished mothers. Our data are consistent with the hypothesis that undernutrition may be an important cause of diabetes mellitus type II.

Blockade of the 32P phosphate flush of pancreatic beta cells from adult rats who received a low-protein diet during early lactation

In order to study the effect of nutrition on the onset of disturbances in Wistar rat pancreatic beta cells, we compared the effects of a low protein diet (8 per cent protein) and a normal protein diet (25 per cent protein) supplied to the dams (6 in each group) during the first 12 days of lactation. The parameter evaluated was the beta cells phosphate flush in response to stimulatory concentration of glucose (16.7 mM) of isolated islets of Langerhans from 60-day old pups. Using a collagenase digestion technique, islets were isolated from the pups and the 32P fractional outflow rate (FOR) of the beta cells was used as a metabolic index in both experimental groups (N = 36). We observed that although the weights of the pups of the two groups were not significantly different at 60 days of age (control = 186 +/- 18 g; undernourished during lactation = 179 +/- 19 g), the typical phosphate flush response (FOR = 2.4 +/- 0.4 per cent /min) to a stimulatory glucose concentration (16.7 mM) was abolished in the rats from undernourished mothers. Our data are consistent with the hypothesis that undernutrition may be an important cause of diabetes mellitus type II