EFFECT OF GALANIN ON BASAL AND STIMULATED SECRETION OF PROLACTIN, GONADOTROPINS, THYROTROPIN, ADRENOCORTICOTROPIN AND CORTISOL IN HUMANS

Galanin enhances both baseline and growth hormone-releasing hormone (G HRH)-induced GH secretion both in animals and in man. Although galanin has a clear influence on the secretion of other anterior pituitary ho rmones in animals, in man it increases prolactin (PRL) slightly but do es not. affect spontaneous thyrotropin (TSH), luteinizing hormone (LW) , follicle-stimulating hormone (FSH) or adrenocorticotropin (ACTH) sec retion. The aim of our study was to verify the effect of galanin on ba sal and releasing hormone-stimulated release of gonadotropins, PRL, TS H, ACTH and cortisol secretion. As GH release has been shown to be inh ibited by corticotropin-releasing hormone (CRH), we also studied the e ffect of CRH on galanin-stimulated GH increase. The effect of porcine galanin (15 mu g/kg iv infused in 60 min) alone and in combination wit h thyrotropin-releasing hormone (TRH, 200 mu g iv bolus), CRH (100 mu g iv bolus) and gonadotropin-releasing hormone (GnRH, 100 mu g iv bolu s) on GH, PRL, TSH, ACTH, cortisol, FSH and LH secretion in seven norm al young women (aged 25-30 years) was studied. Galanin infusion caused an increase in serum GH levels (p < 0.02) but failed to modify signif icantly the spontaneous PRL, LH, FSH, TSH, ACTH and cortisol secretion . The combined administration of TRH, GnRH and CRH caused a significan t increase in PRL (p < 0.02), LH (p < 0.02), FSH (p < 0.02), TSH (p < 0.02), ACTH (p < 0.02) and cortisol (p < 0.05), but not in GH levels. Galanin infusion significantly enhanced the PRL response to TRH+GnRH+C RH administration (p < 0.05), while the releasing hormone-stimulated l evels of LH, FSH, TSH, ACTH and cortisol were not influenced by galani n. The GH release after the combined administration of GAL, TRH, GnRH and CRH was similar to that observed after galanin alone. In conclusio n, the present results support the view that galanin plays a role in t he control of GH and PRL secretion in humans. On the other hand, galan in does not seem to have any influence on the secretion of the other p ituitary hormones in humans. However, a role for galanin in the modula tion of hypophysiotropic neurohormone function at the hypothalamic lev el cannot be ruled out.