Inhibition of dopamine-induced release of growth hormone by thyrotropin-releasing hormone.

The effects of thyrotropin-releasing hormone (TRH) and dopamine (DA) on serum growth hormone (GH) levels were examined in the adolescent male baboon. Intravenously administered DA (40 microgram/kg-min-1 for 20 min) raised serum GH and glucose and lowered serum insulin concentrations but caused no increase in blood pressure. Concomitant intravenous infusion of TRH at 2 doses (96 ng/kg-min-1 and 40 microgram/kg-min-1 for 20 min) blocked the DA-induced increase in serum GH. The relatively low effective doses of TRH used to suppress the DA-induced GH increase suggest an interaction with catecholamines at the hypothalamic and/or pituitary to influence GH release.