Comparative influence of propranolol and verapamil on glycemic control and histamine sensitivity associated with L-thyroxine-induced hyperthyroidism - an experimental study.

The present investigation was undertaken to study the comparative effectiveness of beta-adrenergic antagonist propranolol and calcium channel blocker verapamil on L-thyroxine-induced alteration on glycemic control and histamine sensitivity on rats and guinea pigs, respectively. Injection of L-thyroxine sodium every alternate day for 3 weeks in guinea pigs (75 microg/kg, i.p.) and rats (75 mg/kg, s.c.) produced a condition similar to thyrotoxicosis. Verapamil and propranolol administered daily in the third week along with L-thyroxine to two separate groups of hyperthyroid animals reversed thyroxine-induced loss in body weight, reduction in serum TSH levels, and rise in body temperature. Effect on glucose metabolism and insulin sensitivity was studied on rats. Compared to normal rats, L-thyroxine-treated animals showed a state of hyperglycemia, hyperinsulinemia, impaired glucose tolerance, and insulin resistance. Propranolol (10 mg/kg, i.p.) treatment significantly decreased fasting serum glucose levels without affecting serum insulin levels, AUC glucose, and K(ITT) values. Treatment with verapamil (5 mg/kg, i.p.) significantly reduced fasting serum glucose and insulin levels, AUC glucose, and significantly increased K(ITT) values. Effect of propranolol (15 mg/kg, orally) and verapamil (20 mg/kg, orally) treatment on histamine sensitivity was studied on L-thyroxine-treated guinea pigs. Compared to normal guinea pigs, L-thyroxine-treated guinea pigs showed an increased sensitivity to histamine-induced asphyxia. Verapamil treatment reversed this increased histamine sensitivity while propranolol aggravated it. In conclusion, compared to propranolol, verapamil has advantageous effects on glucose metabolism, insulin and histamine sensitivity and could therefore be a valuable addition as an adjunctive therapy option currently available for thyrotoxicosis associated with diabetes and/or anaphylaxis.