Effects of galanin and leptin on gonadotropin-releasing hormone-stimulated luteinizing hormone release from the pituitary.
BACKGROUND
A number of peptides regulate luteinizing hormone (LH) release. In some cases, these peptides exert an effect at the pituitary, to directly regulate LH release and/or to modulate the effects of gonadotropin-releasing hormone (GnRH). A link between nutrition and reproductive function is well established. In this study we investigated the effects of two peptides associated with appetite control, galanin and leptin, on the regulation of LH release from the pituitary.


METHODS
Using perifused anterior pituitary tissue from freely fed rats, we investigated the effect of galanin on basal LH release and GnRH-stimulated LH release from pituitaries in a high-estrogen (proestrus) and a low-estrogen (metestrus) environment. In addition, we examined the effect of galanin on LH release following GnRH self-priming. The effect of inhibiting protein synthesis, with cycloheximide, was also studied under these conditions. Finally, the effects of leptin alone and on a galanin-modulated LH response were investigated.


RESULTS
There was no detectable effect of leptin, either alone or in conjunction with galanin. We observed that galanin enhanced GnRH stimulation of LH secretion, an effect that was dependent on protein synthesis and on an estrogenized environment. In addition, importantly, galanin also enhanced the LH response in GnRH self-primed pulses.


CONCLUSIONS
Our results provide further details on the effect of galanin on the LH surge, particularly the effect on the response to pulsatile GnRH and the effect of protein production, and thereby indicate a means by which appetite- and nutrition-related peptides may act on the ovulatory cycle at the pituitary.
Peters
Elke E M
EE
Department of Obstetrics and Gynaecology, Christchurch School of Medicine and Health Sciences, University of Otago, New Zealand.
Towler
Kathryn L
KL
Mason
Drusilla R
DR
Evans
John J
JJ
D000818:Animals; D001066:Appetite / Q000502:physiology; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D005298:Fertility; D019004:Galanin / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology; D066298:In Vitro Techniques; D020738:Leptin / Q000502:physiology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D008686:Metestrus; D009747:Nutritional Physiological Phenomena; D010477:Perfusion; D010903:Pituitary Gland, Anterior / Q000378:metabolism* / Q000502:physiology; D011359:Proestrus; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
D020738:Leptin; D011500:Protein Synthesis Inhibitors; D007987:Gonadotropin-Releasing Hormone; D019004:Galanin; D007986:Luteinizing Hormone; D003513:Cycloheximide