| Abstract: | Experiments were conducted in trained, conscious dogs fitted with an indwelling portal catheter. Radioenzymatic methods were employed for the quantitative measurement of plasma-free serotonin and catecholamines. An injection of ovine growth hormone (GH, 100 micrograms/kg) or an equimolar amount of somatostatin (somatotropin release inhibitory factor, SRIF, 7.5 micrograms/kg) into a saphenous vein led, within the first 15 min, to a transient but significant increase in plasma serotonin and a decrease in the concentrations of dopamine, norepinephrine, and epinephrine. The changes were frequently in excess of 40% of baseline values, and were found only in the portal and not in the peripheral circulation. When the animals were pretreated with an antiserum specifically directed against SRIF, GH surges no longer caused alterations in the portal levels of biogenic amines. Thus, the effects of spike concentrations of GH on plasma serotonin and catecholamines are apparently mediated by SRIF, a novel and unexpected function for a hormone that is known as an inhibitor of GH secretion. |
