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.
- growth hormone