Effect of the dopamine receptor blocking agent pimozide on the growth hormone response to arginine and exercise and on the spontaneous growth hormone fluctuations.

Pimozide, a specific blocker of dopamine receptors, was administered orally to 10 diabetics for 2 days before an arginine-hydrochloride infusion. In 8 healthy volunteers and 20 diabetics exercise tests on a bicycle ergometer were performed with a load of 100 Watts and 50 Watts respectively without or after a single dose of pimozide 30 min before the test. In 4 male diabetics day profiles of growth hormone (GH) were estimated without and during treatment with pimozide for 4 days. The arginine and exercise induced GH release was found to be significantly lowered by pimozide, whereas the marked spontaneous fluctuations in the diabetics were even enhanced by pimozide. These data support the concept of the involvement of dopaminergic stimulation in the response of GH to arginine and exercise. The spontaneous fluctuations of GH, however, seem to be regulated by other neuroendocrine mechanisms.