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Effects of melatonin treatment on the gonadotropin‐releasing hormone neuronal system and on gonadotropin secretion in male mink, Mustela vison, in the presence or absence of testosterone feedback
Author(s) -
NToumi F.,
Martinet L.,
MondainMonval M.
Publication year - 1994
Publication title -
journal of pineal research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.881
H-Index - 131
eISSN - 1600-079X
pISSN - 0742-3098
DOI - 10.1111/j.1600-079x.1994.tb00077.x
Subject(s) - medicine , endocrinology , melatonin , mink , testosterone (patch) , luteinizing hormone , castration , gonadotropin , biology , gonadotropin releasing hormone , follicle stimulating hormone , hypothalamus , hormone , ecology
NToumi F, Martinet L, Mondain‐Monval M. Effects of melatonin treatment on the gonadotropin‐releasing hormone neuronal system and on gonadotropin secretion in male mink, Mustela vison, in the presence or absence of testosterone feedback. J. Pineal Res. 1994: 16: 18–25. Abstract The effects of subcutaneous melatonin capsules on the gonadotropin‐releasing hormone (GnRH) immunoreactive (ir) system and the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) have been tested in intact, castrated, and castrated adult male mink supplemented with testosterone. Animals were transferred in July, i.e., during the period of sexual rest, under a daily light: dark cycle of 16‐hr light and 8‐hr darkness and studied over 13 weeks. GnRH (ir) perikarya, visualized by immunocytochemistry, were counted on serial coronal sections from the diagonal band of Broca to the infundibulum. Serum FSH and LH concentrations were measured by radioimmunoassay. In intact mink, melatonin induced a significant increase in the number of (ir) perikarya and in FSH and LH concentrations 3 and 8 weeks, respectively, after melatonin capsule implantation. In castrated mink, the number of perikarya and the concentrations of FSH, which had increased within 2 weeks after castration, did not change during melatonin treatment. In contrast, the concentrations of LH, which were not altered by castration, increased 3–6 weeks after the onset of melatonin administration, suggesting a stimulation of GnRH release. In castrated testosterone‐treated mink, the number of perikarya was increased as in castrated males, but the elevation of FSH in response to castration was prevented. Within 2 weeks after melatonin capsule implantation, the concentrations of FSH decreased while those of LH remained low, indicating an inhibition of GnRH release. These results show that testosterone modulates the effect of melatonin on the activity of the GnRH–gonadotropin system.