Further Observations on Hormonal Support of Pregnancy in the Ovariectomized Rabbit

Abstract

While the necessity for progesterone administration throughout pregnancy in the ovariectomized rabbit is not questioned, the roles of 20oc-dihydroprogesterone and oestradiol are stilI in doubt.20oc-dihydroprogesterone was shown to be a weak inducer of implantation with less than one-tenth the potency of progesterone. The significance of its high level of production on the day after mating remains obscure.In combination with the earlier results of Kwun and Emmens (1974), further work with oestradiol suggests that at no stage is it clearly needed for successful maintenance of pregnancy. However, in low doses (0·125-O·2Ilg/day prior to implantation, 0·2 rising to 1·6Ilg, or remaining at 0·2Ilg/day thereafter) it produced slight but sometimes significant improvements in implantation and foetal development percentages.Birth processes were abnormal if progesterone injections were continued beyond day 29. Foetuses were most frequently retained in utero or born dead after a somewhat prolonged pregnancy. The cessation of injections on day 29, whether or not a low dosage of 0·2 Ilg of oestradiol per day were continued, resulted in 94-98 % normal parturition, but the percentage of live births was stilI significantly below that of controls unless oestradiol was given.

Effects of Progesterone on the Oestrogen-Stimulated Uterus: a Comparative Study of the Mouse, Guinea Pig, Rabbit and Sheep

“…In the ewe and guinea pig the data considered were for the first third of pregnancy, before significant placental P secretion occurs. The doses employed were sufficient when given once daily to maintain gestation in a high proportion of ovariectomized mice (Humphrey 1967;Miller 1978), guinea pigs (Deansley 1960), rabbits (Kwun and Emmens 1975) and sheep (Bindon 1971;Miller et af. 1977a).…”

Hormonal regulation of lysosomal hydrolases in the reproductive tract of the rabbit

“…The antagonistic effects of progesterone and oestradiol on the production of lysosomal hydro¬ lases are comparable to the inhibition of capacitation by progesterone (Chang, 1970;Plotka & Williams, 1971) and the depression of implantation by oestrogen (Kwun & Emmens, 1975). Some of the hormonally regulated enzymes may participate in preparing the embryo or uterus for implantation or assist in removing the zona pellucida from the embryo (Hoversland & Weitlauf, 1981).…”

“…Low levels of progestagens (0-5-1-5 mg, progesterone or 20a-dihydroprogesterone) also enhanced capa¬ citation in ovariectomized oestrogen-treated rabbits, and higher levels of progestagen depressed capacitation (Plotka & Williams, 1971). In the ovariectomized rabbit, 0-3 mg progesterone/day was insufficient for implantation (Hafez & Pincus, 1956), but injection of 1 mg progesterone/day was sufficient for normal implantation (Pincus & Werthessen, 1938;Kwun & Emmens, 1975). Proges¬ terone alone maintains pregnancy in the majority of ovariectomized adrenalectomized does, leav¬ ing any significant role for oestrogen in considerable doubt (Kwun & Emmens, 1975).…”

“…Removal of the ovaries or corpora lutea from rabbits interrupts capacitation (Soupart, 1967 ; Plotka & Williams, 1971), implantation and pregnancy (Allen & Corner, 1929). Administration of exoge¬ nous hormones restores capacitation (Soupart, 1967;Hamner, Jones & Sojka, 1968;Chang, 1970;Plotka & Williams, 1971), implantation and the maintenance of pregnancy (Pincus & Werthessen, 1938;Kwun & Emmens, 1975), but the amount and type of exogenous hormones are crucial.…”