Intracerebroventricular administration of melanin-concentrating hormone suppresses pulsatile luteinizing hormone release in the female rat

Melanin-concentrating hormone (MCH) has been reported to be involved in the regulation of feeding behaviour in rats and mice. Because many neuropeptid es that influence ingestive behaviour also regulate reproductive function, the present study was designed to determine if central administration of MC H changes pulsatile secretion of luteinizing hormone (LH) in the rats. Wist ar-Imamichi strain female rats were ovariectomized and implanted with oestr adiol to produce a moderate inhibitory feedback effect on LH release. The e ffects of i.c.v. injections of MCH on LH release were examined in freely mo ving animals. Blood samples were collected every 6 min for 3 h through an i ndwelling cannula. After 1 h of sampling, MCH (0.1, 1 or 10 mu g/animal) or vehicle (saline) was injected into the third cerebroventricle. Because MCH is also reported to affect the hypothalamo-pituitary-adrenal (HPA) axis, w hich in turn, can influence reproductive function, plasma corticosterone co ncentrations were determined in the same animals at 30-min intervals during the first and last hours and every 12 min during the second hour of the 3- h sampling period. When expressed as per cent changes, mean plasma LH conce ntrations after MCH administration were significantly tower in the animals injected with all doses of the peptide compared with vehicle-treated animal s; LH pulse frequency was significantly lowered by 1 mu g of MCH. Per cent changes in mean plasma corticosterone levels were not significantly affecte d by MCH administration. These results in oestradiol-treated ovariectomized rats indicate that central MCH is capable of inhibiting pulsatile LH secre tion. We have previously shown that 48-h fasting suppresses pulsatile LH re lease in the presence of oestrogen, Take together, these results raise the possibility that MCH could play a role in mediating the suppression of LH s ecretion during periods of reduced nutrition.