Effect of transdermal clonidine on the endocrine responses to insulin-induced hypoglycemia in essential hypertension.

Clonidine hydrochloride via the central nervous system lowers blood pressure, inhibits ACTH and catecholamine release, and stimulates growth hormone secretion. To evaluate the effect of this drug on the release of glucoregulatory hormones during hypoglycemia, we studied the responses to insulin-induced hypoglycemia (0.1 units/kg) in 10 patients with mild essential hypertension before and after treatment for 16 weeks with transdermal clonidine. Clonidine significantly lowered blood pressure, basal plasma norepinephrine levels, and epinephrine and renin activity but did not affect basal growth hormone concentrations. Clonidine significantly reduced the norepinephrine and epinephrine responses to hypoglycemia (norepinephrine AUC from 207 +/- 16 SE to 156 +/- 25 nmol/L/min, epinephrine from 157 +/- 28 to 99 +/- 29 nmol/L/min; both p less than 0.05) and increased the growth hormone response (AUC from 763 +/- 148 ng/min/ml to 1164 +/- 292 ng/min/ml; p less than 0.05) but did not affect the cortisol response or the magnitude or rate of glucose recovery from hypoglycemia. Thus transdermal clonidine has several effects on glucose counterregulatory hormones that do not significantly alter insulin sensitivity or impair recovery from hypoglycemia.