Short term pirenzepine treatment is ineffective in suppressing 24-h growth hormone secretion in type 1 diabetes mellitus.

Large doses of pirenzepine given at bedtime suppress nocturnal GH secretion and abolish dawn phenomenon. As GH suppression may be beneficial in diabetic subjects we have investigated the effect of routine doses of pirenzepine on GH secretion in 9 type 1 diabetics. In the acute study pirenzepine 20 mg i.v. administered 15 min before GHRH 80 micrograms i.v. completely inhibited GHRH-induced GH response and the peak GH values were reduced from 66.3 to 9.2 ng/ml, P < 0.005. In the chronic study pirenzepine was given in a daily dose of 75 or 150 mg for 4 days and GH was measured hourly during 24-h study before and on the fourth day of pirenzepine administration. GH secretion calculated as area under curve (AUC) was not affected by pirenzepine and the values of AUC were: 139 ng/ml per h (the control 24-h study) and 123 ng/ml per h (pirenzepine 75 mg) and 303 ng/ml per h (pirenzepine 150 mg). Mean plasma glucose was not changed by pirenzepine. GH secretion calculated as AUC and mean 24-h GH level did not correlate with metabolic control of diabetes assessed by HbA1. It is concluded that routine doses of pirenzepine do not suppress GH hypersecretion in type 1 diabetic subjects and therefore this agent does not seem suitable for the purpose of 24-h GH suppression in type 1 diabetes mellitus.