Failure of somatostatin antiserum to reverse histamine-induced inhibition of pulsatile growth hormone secretion

We attempted to determine whether the suppression by histamine of spontaneous episodic growth hormone (GH) secretion is mediated by an augmented release of somatostatin (SS). Adult male rats were passively immunized against SS by the injection of a specific goat anti-SS antibody. Plasma GH levels in rats bearing indwelling catheters were measured at 15-min intervals for 4 h. Histamine (0.1 mumol/rat) was administered intracerebroventricularly (i.c.v.) 1 h after the start of the experiment and once an hour for the next 2 h. Anti-SS serum (2 ml) was injected 2 h after the beginning of the experiment to two groups of rats, one given saline i.c.v. and the other histamine i.c.v. Histamine was able to suppress not only spontaneous GH secretion but also the antiserum-stimulated GH release. These data suggest that histamine inhibiton of GH is not mediated by SS but probably by a reduction of GH-releasing hormone or some other stimulatory signal.