Hypophysectomy does not alter the effects of somatostatin or growth hormone on canine splanchnic biogenic amine release

We have demonstrated previously that growth hormone (GH) and somatostatin (somatotropin release inhibitory factor, SRIF) exert comparable effects on the release of splanchnic biogenic amines. The purpose of the present investigation was to study further the response of the two hormones and see whether the similarity persists in dogs completely deprived of endogenous GH. Experiments were conducted in seven hypophysectomized dogs fitted with an indwelling portal catheter. Two to 4 weeks after surgery the responsiveness of their catecholaminergic neurons was tested by an injection of human beta-endorphin (20 micrograms/kg); it caused a rise in portal catecholamine levels equivalent to that seen in intact dogs. Then the effect of a spike concentration of SRIF or GH on hepatic portal and peripheral levels of free serotonin and catecholamines was studied, all by radioenzymatic methods. The intravenous injection of ovine GH (100 micrograms/kg) or equimolar amounts of SRIF (7.5 micrograms/kg) produced in the hepatic portal circulation a transient but statistically significant rise of serotonin and a concomitant reduction in the concentration of dopamine, norepinephrine, and epinephrine. No changes were found in the peripheral circulation. The response patterns to SRIF or GH were virtually identical, which is in keeping with our other data, suggesting that the effect of GH on splanchnic biogenic amine secretion is SRIF-dependent and mediated by SRIF-containing neurons.(ABSTRACT TRUNCATED AT 250 WORDS)