A central action of alpha-melanocyte-stimulating hormone on serum levels of LH and prolactin in rats.
We have investigated the effect of administration of alpha-MSH into the median eminence (ME) of rats on the release of LH and prolactin. Continuous infusion of alpha-MSH (0.5 micrograms/h) into the ME from the afternoon of the second day of dioestrus and over the 24 h of pro-oestrus inhibited the preovulatory LH and prolactin surge and the occurrence of ovulation. This inhibitory effect on LH and prolactin release was also observed in chronically ovariectomized rats given a single injection of alpha-MSH (1 micrograms/ml per rat) into the ME (blood samples were collected 0, 20, 60, 90, 105 and 120 min after injection). The intraperitoneal injection of the dopamine receptor blocker, haloperidol (2 mg/kg), 30 min before the injection of alpha-MSH into the ME prevented the inhibitory effect of alpha-MSH on the release of LH and prolactin. These results suggest that hypothalamic alpha-MSH might be involved in the regulation of LH and prolactin release via the tuberoinfundibular dopaminergic system and that this system also modifies the serum concentrations of alpha-MSH.
Scimonelli
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Departmento de Farmacología, Facultad de Ciencias, Universidad Nacional de Córdoba, Argentina.
Celis
M E
ME
D000818:Animals; D015259:Dopamine Agents / Q000494:pharmacology; D004971:Estrus; D005260:Female; D006220:Haloperidol / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008473:Median Eminence / Q000187:drug effects / Q000378:metabolism*; D010052:Ovariectomy; D010060:Ovulation / Q000187:drug effects; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D000521:alpha-MSH / Q000494:pharmacology*
D015259:Dopamine Agents; D000521:alpha-MSH; D011388:Prolactin; D007986:Luteinizing Hormone; D006220:Haloperidol