Release of LH in response to alpha-MSH administration.
The aim of the present study was to determine the effect of alpha-MSH on serum LH in order to obtain some clues about the possible, mechanism by which the peptide modifies gonadotropin secretion. Intact female rats treated with alpha-MSH on diestrus 2 afternoon exhibited an increase in serum LH levels at 18 hr on proestrus and an elevated number of ova per rat the day of estrus when compared with saline-treated controls. Moreover, the peptide administered in chronically ovariectomized (CHR-OVX) rats treated with estradiol benzoate (EB) plus low doses of progesterone (P), increased LH in serum as well as P serum levels when compared with levels in CHR-OVX animals treated with EB plus P and saline solution instead of alpha-MSH. It has been shown that LH release is blocked by OVX and adrenalectomy (ADX) on the afternoon of proestrus; this blockade was reversed by an injection of alpha-MSH at the time of the operation. Measurements of P in ADX-OVX animals treated with alpha-MSH showed that P serum levels were maintained for longer periods of time when compared with the P serum levels of ADX-OVX animals treated with saline. On the other hand, alpha-MSH infused into CHR-OVX rats treated with low doses of EB, which can lower serum LH levels, lowered the serum LH even more, although the serum P levels were increased. Finally alpha-MSH did not affect the serum LH levels in diestrous rats. The present results demonstrated that alpha-MSH influences the release of LH by modifying the release and/or the degradation of P. This P, in turn, modifies LH serum concentrations, having either a stimulatory or inhibiting effect on the release of LH, apparently depending on the time period it remains high in serum.
D000315:Adrenalectomy; D000818:Animals; D004031:Diestrus; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D009074:Melanocyte-Stimulating Hormones / Q000008:administration & dosage / Q000494:pharmacology*; D010052:Ovariectomy; D010060:Ovulation / Q000187:drug effects; D011359:Proestrus; D011374:Progesterone / Q000494:pharmacology; D051381:Rats
D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D009074:Melanocyte-Stimulating Hormones