Glucose intolerance and impaired insulin release following 6-hydroxydopamine administration to intact rats

Postoperative insulin secretion is decreased in patients with preoperative insulin resistance

BACKGROUND

Postoperative hyperglycemia is associated with increased rate of surgical site infection, renal failure, and cardiovascular events. The study of insulin sensitivity state before surgery could help in treating postoperative hyperglycemia and preventing iatrogenic hypoglycemia. We studied the postoperative insulin secretion in patients who have a low insulin sensitivity (IR) before surgery compared to patients with normal preoperative insulin sensitivity (IS).

MATERIALS AND METHODS

Forty-two consecutive patients, undergoing abdominal surgery, underwent preoperative sequential hyperglycemic-euglycemic clamp (SHEC) in order to measure insulin secretion and to screen patients with low insulin sensitivity (IR) or with normal insulin sensitivity (IS). Patients had been randomized to receive either general anesthesia with epidural or PCA.

RESULTS

Postoperative insulin secretion in IR patients is decreased compared to IS (P = 0.059) and to IR before surgery regardless to the type of analgesia (P < 0.001). In the IS group, postoperative insulin secretion depends on type of analgesia. It is increased when using PCA and decreased when using epidural (P < 0.05). Blood glucose increased after surgery in both IS an IR (P < 0.001). Patients with preoperative insulin resistance had a higher glycemia before and after surgery (P < 0.001). Blood glucose levels were comparable between PCA and epidural patients (P = 0.450).

CONCLUSION

Insulin secretion is reduced in IR regardless the type of anesthesia. PCA increases insulin secretion, whereas epidural decreases it in patients with normal insulin sensitivity. These findings implicate that after surgery insulin administration is advisable in patients with preoperative insulin resistance while it should be given cautiously in those with normal preoperative insulin sensitivity.

Glucagon-like peptide-1 reduces pancreatic β-cell mass through hypothalamic neural pathways in high-fat diet-induced obese rats

We examined whether glucagon-like peptide-1 (GLP-1) affects β-cell mass and proliferation through neural pathways, from hepatic afferent nerves to pancreatic efferent nerves via the central nervous system, in high-fat diet (HFD)-induced obese rats. The effects of chronic administration of GLP-1 (7–36) and liraglutide, a GLP-1 receptor agonist, on pancreatic morphological alterations, c-fos expression and brain-derived neurotrophic factor (BDNF) content in the hypothalamus, and glucose metabolism were investigated in HFD-induced obese rats that underwent hepatic afferent vagotomy (VgX) and/or pancreatic efferent sympathectomy (SpX). Chronic GLP-1 (7–36) administration to HFD-induced obese rats elevated c-fos expression and BDNF content in the hypothalamus, followed by a reduction in pancreatic β-cell hyperplasia and insulin content, thus resulting in improved glucose tolerance. These responses were abolished by VgX and SpX. Moreover, administration of liraglutide similarly activated the hypothalamic neural pathways, thus resulting in a more profound amelioration of glucose tolerance than native GLP-1 (7–36). These data suggest that GLP-1 normalizes the obesity-induced compensatory increase in β-cell mass and glucose intolerance through a neuronal relay system consisting of hepatic afferent nerves, the hypothalamus, and pancreatic efferent nerves.

Adrenalectomy and chemical sympathectomy by 6-hydroxydopamine. Effects on basal and stimulated insulin secretion

Influences of the sympatho-adrenal system on basal and stimulated insulin secretion were studied in vivo in the conscious mouse and rat. In the mouse, adrenalectomy or chemical sympathectomy, induced by 6-hydroxydopamine, lowered basal insulin concentrations moderately. A marked depression of basal insulin concentration (about 50%) was seen after the combined treatment of chemical sympathectomy and adrenalectomy. In short-term experiments in mice, insulin secretion stimulated by glucose or the cholinergic agonist carbachol was enhanced after chemical sympathectomy and/or adrenalectomy, whereas insulin release induced by the synthetic octapeptide of cholecystokinin (CCK-8) was inhibited. The promoting influences on the insulin secretory response to carbachol displayed a rapid development whereas those to glucose developed more slowly. In contrast, the inhibiting effect on CCK-8 stimulated insulin release vanished with time. The insulin secretory response to the beta 2-adrenoceptor stimulator, terbutaline, was increased after chemical sympathectomy, unaffected by adrenalectomy, and decreased after chemical sympathectomy plus adrenalectomy. The glucose elimination rate after 6 weeks of chemical sympathectomy was increased in mice and decreased in rats. The insulin secretory response to glucose was enhanced in mice, whereas it tended to diminish in rats after long-term sympathectomy. In conclusion, the sympatho-adrenal system is involved in regulation of basal insulin concentrations in the mouse, and apparently is of great importance for stimulated insulin secretion; the influence being dependent on the nature of the secretagogue.

Influence of the sympatho-adrenal system and somatostatin on the secretion of insulin in the rat

1. The effects of somatostatin on insulin secretion in anaesthetized rats subjected to different manipulations of the sympatho-adrenal system have been investigated.2. Somatostatin (0.1 mug/min) inhibited the secretion of insulin in intact rats both in the basal state and after inducing an enhanced insulin release by infusion of the alpha-adrenoceptor-blocker phentolamine.3. Combined surgical splanchnicotomy and adrenalectomy caused an increase in the basal plasma insulin concentration. Somatostatin (0.1 mug/min) inhibited basal insulin release also in these rats. After infusion of phentolamine, however, the dose of somatostatin had to be raised five fold (0.5 mug/min) to achieve a comparable inhibition of insulin release. On the other hand, a similar rate of insulin secretion induced by glucose in intact rats could be inhibited by the lower dose of somatostatin.4. Administration of the beta-adrenoceptor-blocking agent propranolol to splanchnicotomized-adrenalectomized rats lowered basal insulin secretion to the same level as seen in intact rats. In these beta-adrenoceptor-blocked rats somatostatin (0.1 mug/min) inhibited insulin release both in the presence and absence of alpha-adrenoceptor blockade.5. Rats subjected to chemical sympathectomy through pre-treatment with 6-hydroxydopamine together with adrenalectomy displayed plasma insulin concentrations slightly above the normal range, but the values were much lower than in splanchnicotomized-adrenalectomized rats. Infusion of phentolamine to the chemically sympathectomized rats did not further increase insulin secretion, and somatostatin (0.1 mug/min) depressed insulin release both in the absence and presence of alpha-adrenoceptor blockade.6. It is suggested that an inhibitory tone exerted by the splanchnic nerves modulates the basal insulin secretion in the rat. Somatostatin and the sympathoadrenal system show a complex interaction on the insulin cells in that the sensitivity to somatostatin in splanchnicotomized-adrenalectomized rats with intact beta-adrenoceptors is decreased in the presence of the alpha-adrenoceptor-blocker phentolamine. The exact mechanism behind this decreased sensitivity remains unclear.

Effect of chemical sympathectomy on glycogen storage in rat skeletal muscle in thermal trauma

The glycogen storage in rat skeletal muscle is reduced after a 20% third degree burn. The reason is probably a relative deficiency of insulin caused by insulin resistance at the tissue level. Posttraumatically increased sympatho-adrenal function has been suspected to cause this insulin resistance. In an earlier study, however, it has been shown that adrenal demedullation has no effect on the glycogen storage. In the present investigation an attempt was made to assess the importance of the increased peripheric sympathetic activity. Muscle glycogen, serum insulin and blood glucose were determined at the end of a glucose infusion after infliction of a burn both in 6-hydroxy-dopamine treated rats and rats with an intact peripheric sympathetic nervous system. It was found that a chemical sympathectomy did not improve the glycogen storage. The result indicates that the increased activity of the sympatho-adrenal system after a burn is not the main cause of the reduced skeletal muscle glycogen storage.

Interactions of acetylcholine and epinephrine on the dynamics of insulin release in vitro

An in vitro system for perifusion of rat pancreatic islets has been utilized to define the effects of epinephrine on acetylcholine-induced insulin release over varying concentrations of the two agents. Perifusion of islets with epinephrine before challenge with acetycholine produced marked enhancement of both phases of cholinergically induced insulin release; enhancement of the first phase being more marked with increase in acetylcholine concentration and the converse being observed with the second phase. Perifusion of islets with epinephrine during stimulation with acetylcholine produced inhibition of insulin release, an effect dependent upon the concentration of epinephrine and of acetylcholine. There was an order of difference in the acetycholine concentration needed to overcome significant epinephrine-mediated inhibition of the first phase of insulin release (5 X 10(-4) mug/ml) and that needed to overcome inhibition of the second phase (5 X 10(-3) mug/ml). Comparison of the effects of various concentrations of epinephrine on glucose- and acetyl-choline-induced insulin release revealed that epinephrine was a less potent inhibitor of the first phase of acetylcholine-induced insulin release than of the first phase of glucose-induced insulin release. These data provide some insight into the potential interactions between cholinergic and adrenergic autonomic systems in modifying insulin release.