Serotonin, a Neurotransmitter Involved in the Regulation of Luteinizing Hormone Release*

Abstract

The involvement of serotonin (5-HT) in the regulation of LH secretion is discussed on the basis of experimental and physiological models. The role of 5-HT on low amplitude pulsatile LH release in male rats is not yet clear, in spite of the fact that recent results suggest a weak permissive role. In ovariectomized rats, 5-HT expresses a negative influence on the increased rate of LH release, which is converted into a stimulatory effect by pretreatment of the animals with E2. Moreover, in castrated female rats there is a morning/afternoon oscillatory pattern in 5-HT metabolism of brain areas associated with the control of LH secretion including the hypothalamus. In this area, the fluctuation is modulated by E2 in such a way that the peak of 5-HT neural activity occurs simultaneously with the induced afternoon discharge of LH. On the other hand, P enhances the amplitude of the oscillation of hypothalamic 5-HT metabolism concomitantly with a potentiation of the induced LH surge. This facilitatory role of 5-HT upon phasic LH discharge is also evident in intact female rats. The preovulatory surge of LH is accompanied by an increased hypothalamic and, more precisely, ME 5-HT turnover. Furthermore, 5-HT stimulates in vitro LHRH release from the ME. Serotonergic nuclei located in the brain stem seem to mediate this effect.