Function of serotonin in physiologic secretion of growth hormone and prolactin: Action of 5,7-dihydroxytryptamine, fenfluramine and p-chlorophenylalanine

Growth hormone (GH) and prolactin secretory patterns in male rats chronically implanted with venous cannulae were studied in response to treatments known to acutely or chronically deplete central serotinin (5-HT) or to permanently destroy a high proportion of 5-Ht neural structures. Spontaneous prolactin secretion was little affected by chronic 5-HT depletion produced by 5,7-dihydroxytryptamine (5,7-DHT) or parachlorophenylalanine (PCPA). Acute 5-HT release induced by fenfluramine produced sustained prolactin secretion in intact and 5-HT-depleted rats. GH secretion was inhibited by PCPA, and for 3 days following 5,7-DHT, but was normal by 7 and 21 days. Acute 5-HT release stimulated by fenfluramine unexpectedly inhibited GH in intact and 5-HT-depleted rats. It is concluded that 5-HT is a potent facilatory neurotransmitter for prolactin; and its appears to have both facilitatory and inhibitory effects on GH. Recovery of GH secretory patterns within 7 days of 5,7-DHT treatment indicates that mechanisms act rapidly to compensate for depletion of 5-HT, and that it is difficult to achive functional depletion of 5-HT for more than a few days.