LUTEAL REGRESSION INDUCED BY ARACHIDONIC ACID IN THE PSEUDOPREGNANT RABBIT

Abstract

Administration of prostaglandin F2\g=a\(PGF2\g=a\)to pseudopregnant rabbits results in a rapid decline in luteal weight and progesterone secretion (Scott & Rennie, 1970; Gutknecht, Duncan & Wyngarden, 1971). There is evidence that PGF2\g=a\ may be theuterine luteolysin' in other species, in particular the sheep, guinea- pig and hamster (see Pharriss, Tillson & Erickson, 1972). Indomethacin, a potent inhibitor of prostaglandin synthesis, has been shown to prolong the functional lifespan of CL in the pseudopregnant rabbit (O'Grady, Caldwell, Auletta & Speroff, 1972). The fact that this prolongation of luteal life is similar to that produced by hysterectomy led O'Grady and co-workers to suggest that PGF2\g=a\may be the uterine luteolysin in the rabbit. As arachidonic acid (5,8,11,14-eicosatetraenoic acid) is a normal precursor of PGF2\g=a\and PGE2\g=a\(Bergstr\l=o"\m,Carlson & Weeks, 1968), it might be expected to produce luteolytic effects in mammals. The purpose of this study was to determine the effect of archidonic acid on luteal maintenance in pseudopregnant rabbits and to determine whether or not the uterus is essential for the mediation of such effects. Forty New Zealand white rabbits, weighing 3 to 4 kg each, were used for this study. They were housed in isolated cages for at least 15 days before being injected intravenously with 50 i.u. HCG (Antuitrin-S, Parke-Davis) for the induction of pseudopregnancy. The day of injection was designated Day 0 of