Effect of nifedipine and enalapril on insulin-induced glucose disposal in spontaneous hypertensive and diabetic rats

A Study to Assess the Therapeutic Effect of Enalapril on Olanzapine Induced Metabolic Syndrome in Wistar Rats

INTRODUCTION

Metabolic Syndrome (MS) is a complex of risk factors for the development of cardiovascular complications and Type 2 Diabetes Mellitus (DM). Pharmacological management of the condition is complex, as multiple drug groups have to be used, as the syndrome itself is multi faceted. Angiotensin Converting Enzyme Inhibitors (ACEIs) are chiefly used to manage the hypertensive component of the syndrome. However, recent studies have shown that these drugs may have a role in the non hypertensive aspects of the syndrome as well.

AIM

To evaluate the therapeutic effect of enalapril on total body weight, random blood glucose and serum lipid profile in a rodent model of olanzapine induced MS.

MATERIALS AND METHODS

Three different dosages (1 mg/kg/day, 10 mg/kg/day and 20 mg/kg/day) of oral enalapril were administered (for three weeks) in albino wistar rats, which received prior intra peritoneal olanzapine (for three weeks), and compared against control (normal saline) and standard (olanzapine only and enalapril only) groups. Parameters like total body weight, random blood glucose and serum lipid profile were measured at baseline, at three weeks and at six weeks.

RESULTS

Enalapril at 20 mg/kg/day was found to be effective in reversing the weight gain, hyperglycaemia and hypercholesterolaemia, without any changes in triglycerides, High Density Lipoprotein (HDL) and Low Density Lipoprotein (LDL). 10 mg/kg/day of enalapril prevented any further rise in body weight, blood glucose, total cholesterol and serum triglycerides, after olanzapine was stopped. 1 mg/kg/day of enalapril was ineffective.

CONCLUSION

High dose of enalapril may be considered as a component of therapeutic regimens to combat weight gain, hyperglycaemia and dyslipidaemia seen in MS, in addition to its antihypertensive utility. Further rodent and clinical studies may be required to ascertain the same.

Immediate but not long-term administration of nicardipine inhibits tolbutamide-induced insulin secretion from rat pancreatic beta cells

OBJECTIVES

Calcium channel blockers alter glucose homeostasis, but sufficient data regarding this effect in healthy animals have not been provided. We test the effect of nicardipine on beta cell function in healthy rats.

METHODS

Islets from Sprague-Dawley rats were coincubated with nicardipine, tolbutamide, or their combination for 1 hour. Insulin secretion was measured by radioimmunoassay. The rats were given nicardipine, tolbutamide, or their combination by intravenous injection. Intravenous glucose tolerance tests were performed after the first drug administration and 4 weeks later. Pancreata were excised for assessment of insulin content and immunohistochemical staining in the end.

RESULTS

Nicardipine markedly inhibited not only the insulin secretion by islets per se but also that enhanced by tolbutamide in vitro. Blood glucose was reduced by tolbutamide in vivo but elevated by nicardipine abruptly in parallel with retarded insulin secretion. Long-term administration of nicardipine altered neither fasting blood glucose level nor fasting serum insulin level, whereas pancreatic insulin content was unmodified despite that nicardipine caused shrunken islets with weak immunoreactivity of beta cells by immunohistochemistry.

CONCLUSIONS

In healthy rats, immediate administration of nicardipine inhibits insulin secretion of beta cells both in vitro and in vivo but does not exert a deleterious effect in vivo after long-term treatment.

PKC-mediated modulation of L-type calcium channels may contribute to fat-induced insulin resistance

Increased intracellular free calcium [Ca2+]i has been noted in adipocytes, platelets, and leukocytes of subjects with insulin resistance syndrome or allied disorders. In rodent studies, measures which increase [Ca2+]i in adipocytes and skeletal muscle are associated with impaired insulin signaling, attributable at least in part to diminished ability of insulin to activate phosphoserine phosphatase-1 (PP-1). In fat-fed insulin resistant rats, pre-treatment with a drug that selectively chelates intracellular calcium eliminates about half of the decrement in insulin-stimulated glucose uptake induced by fat feeding; since this chelator does not influence the insulin sensitivity of chow-fed rats, it is reasonable to suspect that fat feeding boosts [Ca2+]i in skeletal muscle, and that this effect is partially responsible for the associated reduction in insulin sensitivity. Clinical insulin resistance is associated with increased levels of triglycerides and other fatty acid metabolites in muscle fibers; this can give rise to diacylglycerol-mediated activation of PKC, which in turn compromises insulin signaling by triggering kinase cascades that phosphorylate IRS-1 on key serine residues. Yet there is also evidence that, in skeletal muscle, PKC activity up-regulates the function of L-type calcium channels, increasing their maximal conductance while left-shifting their voltage dependence. Thus, the PKC activation associated with fat overexposure might be expected to boost basal [Ca2+]i in skeletal muscle, potentially impeding insulin-mediated activation of PP-1. This hypothesis is consistent with several clinical studies demonstrating that long-acting inhibitors of L-type calcium channels can improve insulin sensitivity in overweight hypertensives; it should be readily testable in rodent models of fat-induced insulin resistance. Since parathyroid hormone can act on adipocytes and muscle to boost [Ca2+]i, mild secondary hyperparathyroidism associated with low calcium intakes and poor vitamin D status may contribute to insulin resistance, consistent with certain clinical and epidemiological findings. Magnesium, often thought of as a mild calcium antagonist, appears to have favorable effects on insulin sensitivity and risk for diabetes, and recent evidence indicates that increases of intracellular magnesium within the physiological range can diminish calcium influx through phosphorylated L-type calcium channels. It will be of interest to determine whether calcium antagonism does indeed underlie the favorable influence of good magnesium status on insulin function. A report that chromium picolinate can induce the plasmalemmal Ca2+-ATPase in smooth muscle cells, raises the possibility that modulation of calcium transport might play a role in the insulin-sensitizing efficacy of bioactive chromium.

Ramipril treatment suppresses islet fibrosis in Otsuka Long–Evans Tokushima fatty rats

We evaluated whether ramipril, one of long-acting ACEIs, has a direct effect on pancreas islets in animal model of type 2 diabetes. OLETF rats were treated with ramipril for 24 weeks. We assessed the body weight, glucose tolerance, and the amount of islet fibrosis. RT-PCR and Western blot analysis of transforming growth factor-beta with its downstream signals were performed from the pancreas. Ramipril treatment remarkably reduced weight gain and the area under the curve of glucose. Islet fibrosis and the expression of TGF-beta with its downstream signal molecules were significantly reduced in the pancreas of ramipril-treated group than in control and paired-feeding group. These beneficial effects of ramipril might be related to the downregulation of TGF-beta and its downstream signals in OLETF rats. To our knowledge, this is the first report suggesting the potential effect of ramipril on the prevention of islet destruction by fibrosis in the animal model of type 2 diabetes mellitus.