The assessment of growth hormone status in normal young adult males using a variety of provocative agents.

Abstract

In adults, there are few data regarding GH responses to provocative stimuli other than insulin-induced hypoglycaemia. We have compared the GH response to four different growth hormone secretagogues and placebo in normal healthy adult males. This was a prospective, randomized, placebo-controlled study in 18 normal male subjects. After an overnight last, an intravenous cannula was inserted into the arm of each subject and a blood sample was taken for GH at -30, -15, and 0 minutes. Four provocative agents (intravenous insulin 0.2 IU/kg; intravenous arginine 20 g/m2 as an infusion over 30 minutes; oral clonidine, either 100 or 200 micrograms; intramuscular glucagon 1 mg) and placebo were administered to each subject in a randomized manner on different days. Further blood samples were taken at 15-minute intervals for 180 minutes for GH estimation. The median (range) GH peak response for each agent was insulin 107.7 (28.1-200) mU/l; arginine 22.3 (3.1-72.9) mU/l; glucagon 42 (11.8-200) mU/l; 100 micrograms clonidine 7.2 (< 1-22.2) mU/l; 200 micrograms clonidine 8.2 (1.1- 88) mU/l and placebo 2.4 (< 1-30.2) mU/l. The peak GH response to insulin-induced hypoglycaemia (ITT) was significantly greater than for any other agent (P < 0.0001). The peak GH response to glucagon was significantly greater than for arginine (P < 0.05), clonidine at 100 and 200 micrograms (P < 0.01) and placebo (P < 0.01). The peak GH response following administration of arginine was significantly greater than for clonidine 100 and 200 micrograms (P < 0.05), and placebo (P < 0.01). The peak GH response following clonidine 200 micrograms was not significantly greater than following clonidine 100 micrograms (P = 0.38) or placebo. On an individual basis two, six and 15 of 18 subjects failed to achieve a peak GH level of > 20 mU/l to glucagon, arginine and clonidine respectively. In complete contrast only one subject achieved a peak response of less than 40 mU/l (28.1 mU/l) to ITT. The most profound GH release is seen after insulin-induced hypoglycaemia. Glucagon appears to be more effective at inducing GH release than arginine. Clonidine at a dose of 100 or 200 micrograms is no more effective than placebo.