The effect of the blockade of alpha-melanocyte-stimulating hormone on LH release in the rat.
We have investigated the effect of blocking alpha-MSH on the release of LH in rats at pro-oestrus. Continuous infusion of Pro-Leu-Gly-NH2 (PLG; 0.2 microgram/h), from the afternoon of dioestrus-2 until the day of oestrus, inhibited LH at pro-oestrus and the next ovulation on the day of oestrus. Plasma alpha-MSH levels decreased significantly in rats treated with PLG. This inhibitory effect on LH release was not observed in rats treated with a continuous infusion of a diluted antiserum against alpha-MSH (0.5 microliter/h, diluted 1/10) from the afternoon of dioestrus-2 until the day of oestrus. On the contrary, the administration of undiluted antiserum against alpha-MSH (0.5 microliter/h) blocked LH release and ovulation. The release of alpha-MSH into the blood was also significantly blocked by this treatment. When serum levels of progesterone were measured at 12.00 and 14.00 h in rats in which alpha-MSH release was blocked by PLG or concentrated antiserum, a significant decrease was observed when compared with the levels of progesterone in control rats. These results show that the blockade of alpha-MSH inhibits LH release and the next ovulation in rats treated with PLG or with concentrated antiserum against alpha-MSH, through a blockade of progesterone of adrenal origin.
Caballero
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Department of Pharmacology, Universidad Nacional de Córdoba, Argentina.
Celis
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D000818:Animals; D005260:Female; D007106:Immune Sera / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000096:biosynthesis* / Q000097:blood; D009075:MSH Release-Inhibiting Hormone / Q000031:analogs & derivatives* / Q000494:pharmacology; D010060:Ovulation / Q000187:drug effects / Q000378:metabolism; D011359:Proestrus / Q000378:metabolism; D011374:Progesterone / Q000097:blood; D051381:Rats; D017208:Rats, Wistar; D000521:alpha-MSH / Q000097:blood / Q000276:immunology / Q000378:metabolism*
D007106:Immune Sera; C055207:prolyl-leucyl-glycine; D011374:Progesterone; D000521:alpha-MSH; D007986:Luteinizing Hormone; D009075:MSH Release-Inhibiting Hormone