Role of serotoninergic neurones in the control of gonadotrophin and prolactin secretion in the rat

Abstract

The role of brain serotonin (5-hydroxytryptamine, 5-HT) in the control of LH, FSH and prolactin secretion was studied in two groups of experimental animals: intact adult male rats and ovariectomized adult female rats. 5-Hydroxytryptophan (5-HTP), a precursor of serotonin synthesis, and fluoxetine, a specific inhibitor of 5-HT uptake, were given either alone or together. 5\ x =r eq-\ Hydroxytryptophan (50 mg/kg) was administered intraperitoneally and fluoxetine (20 \g=m\g/rat) was given into one of the lateral ventricles of the brain. Neither 5-HTP nor fluoxetine given alone affected LH secretion but combined treatment with the two drugs elicited a significant increase in serum LH levels in both intact male and ovariectomized female rats. Fluoxetine and 5-HTP, alone or together, did not modify FSH secretion in either kind of animal. In intact males and in ovariectomized females, 5-HTP induced a significant increase in prolactin release; fluoxetine alone was ineffective. In male animals treated with fluoxetine plus 5-HTP, serum prolactin levels increased but such an increase was lower than that found in the animals treated only with 5-HTP. In ovariectomized rats, the combined treatment induced an increase in serum prolactin levels similar to that found in animals treated with 5-HTP alone.These data suggested that brain serotonin exerts a stimulating effect on LH secretion in both intact male and ovariectomized rats, but that it does not play any role in the control of FSH release in either kind of animal and that central serotoninergic pathways participate in the stimulating control of prolactin release from the anterior pituitary gland. However, some of the data also suggested the possibility of the existence in the brain of serotoninergic systems inhibiting prolactin secretion.

Depending on the Stimulus, Central Serotoninergic Activation by Fenfluramine Blocks or Does not Alter Growth Hormone Secretion in Man

“…A double dose was unable to potentiate the PRL secretion suggesting that the dose employed in this study, commonly used in clinical practice, is already at the maximal action level. A similar serotoninergic stimulatory effect on rat PRL secretion has been previously reported [14,15,40,41].…”

Serotoninergic Involvement in Gonadotropin and TSH Secretion in Normal Cycling and Postmenopausal Women

“…In prepubertal rats, serotonin is capable of stimulating LH and FSH [8], whereas in adult rats the findings are more confusing [7]. But several investigators reported increased LH secretion in rats and ewes due to serotoninergic stimulation [9, 10, 11]. Stimulation of LH secretion is the result of direct action at the pituitary level [11] as well as increased GnRH release from the median eminence [12].…”

“…In ovariectomized rats, activation of central serotonin activity led to an increased LH secretion [9]. Contrary results have also been reported [19, 20] depending on the route of drug administration.…”

Effects of the Intraventricular Administration of 5,7-Dihydroxytryptamine on FSH, LH and Prolactin Secretion in Neonatally Estrogenized Male Rats

“…Administration of 5-HT as intra ventricular [Kamberi et al, 1971] or systemic injection [Lawson and Gala, 1978], or the administration of precursors [Lu and Meites, 1973;Chen and Meites, 1975;Ruzsas et al, 1982] or receptor agonists [Lawson and Gala, 1978;Krulich et al, 1979] increased plasma prolactin levels. Furthermore serotonin up take antagonists potentiate the releasing ef fect of 5-HT precursors [Krulich.…”

“…Some data suggest that 5-HT stimu lates LH secretion [Wuttke et al, 1977;Van de Kar et al, 1980;Chen et al, 1981;Ruzsas et al, 1982] whereas others show the oppo site [Kamberi et al, 1970;Ladosky and Noronha, 1974;Pilotte and Porter, 1979], From the few available data regarding the effects of serotonin on FSH secretion, both an inhibi tory action and no effect have been described [Kamberi et al, 1971;Wuttke et al, 1977;Ruzsas et al, 1982], It has been generally agreed that rats neonatally injected with sex steroids show changes in gonadotropins and prolactin se cretion in adulthood [Mallampatli andJonson, 1973a, b, 1974;Mogiulevski et al, 1978;Aguilar et al, 1984] together with modifica tions in their aminergic systems [Vaccari. 1980;Demurest et al, 1981;Lookingland et al, 1982],…”