Luteolysis induced by a prostaglandin F2alpha analogue occurs independently of prolactin in the rat.
The hypothesis that prolactin exerts a stimulatory dominance over the luteolytic effect of prostaglandin (PG) F2alpha on corpus luteum maintenance and progesterone production was experimentally tested. A dose-dependent effect of the stable PGF2alpha analogue cloprostenol (dose range 200 ng(-5) microg) was found 12 h after s.c. injection, in Day 9 adult pseudopregnant rats: 1) LH receptor mRNA levels, as measured by RNase protection assay, were dramatically decreased (by 67%) by a single s.c. dose of 200 ng cloprostenol; and 2) serum progesterone levels were significantly (p < 0.05) decreased (by 43%) whereas 20alpha-dihydroprogesterone significantly (p < 0.05) increased (by 80%) initially at a 0.5-microg dose of cloprostenol. To study the integrated response to prolactin and PGF2alpha, we investigated the effect of cloprostenol treatment in sterile-mated female rats with or without circulating prolactin. Prolactin secretion was inhibited by s.c. injection of bromocriptine (1 mg) in the morning of the ninth day of pseudopregnancy. A group of rats was left prolactin-depleted; in another group prolactin was reintroduced by adding 8 IU ovine prolactin. It was found that after injection of 0.5 microg cloprostenol the LH receptor mRNA levels and the serum progesterone/20alpha-dihydroprogesterone ratio were not significantly different whether the rats had circulating endogenous/exogenous prolactin or were prolactin-depleted. Therefore, although prolactin exerts a stimulatory influence on both progesterone production and corpus luteum LH receptor gene expression, the conclusion is reached that prolactin alone cannot antagonize the luteolytic effect of PGF2alpha.
Department of Physiology, Umeå University, Sweden. erik.bjurulf@physiol.umu.se
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Bjurulf
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Toffia
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Selstam
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Olofsson
D000818:Animals; D003008:Cloprostenol / Q000008:administration & dosage / Q000494:pharmacology*; D003338:Corpus Luteum / Q000187:drug effects* / Q000502:physiology*; D015237:Dinoprost / Q000031:analogs & derivatives*; D004305:Dose-Response Relationship, Drug; D005260:Female; D011374:Progesterone / Q000097:blood; D011388:Prolactin / Q000494:pharmacology*; D011555:Pseudopregnancy; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011974:Receptors, LH / Q000235:genetics
D012333:RNA, Messenger; D011974:Receptors, LH; D003008:Cloprostenol; D011374:Progesterone; D011388:Prolactin; D015237:Dinoprost