Advancement of Uterine Secretion of Prostaglandin E₂by Treatment with Progesterone and Transfer of Asynchronous Embryos*

Abstract

Effects of treatment with progesterone early after estrus and the age of the blastocyst in the uterus on day-6 postestrus on uteroovarian venous concentration of prostaglandin E2 (PGE2) during days 7-12 postestrus were examined. At estrus, 24 ewes were assigned randomly to mating with fertile rams and daily injections of progesterone from days 1-3 postestrus, mating with fertile rams and daily injections of vehicle from days 1-3 postestrus, no mating, injection of progesterone from days 1-3 postestrus and transfer of a day-10 blastocyst into the uterus on day-6 postestrus, and no mating, injection of vehicle from days 1-3 postestrus and transfer of a day-10 blastocyst into the uterus on day-6 postestrus. PGE2 increased beginning on day 8 in progesterone-treated ewes that received a day-10 blastocyst on day-6 postestrus, but did not increase until day 12 in mated ewes with confirmed pregnancy. PGE2 remained at basal concentrations in mated progesterone-treated ewes (with a day-6 blastocyst on day-6) and showed only a transient rise on day-11 in vehicle-treated ewes which received a day-10 blastocyst on day-6 postestrus. It is concluded that progesterone regulates the ability of the uterus to release PGE2 in response to a blastocyst of appropriate age.