Contrasting effects of oestradiol-17  and human chorionic gonadotrophin on steroidogenesis in the rabbit corpus luteum

Abstract

On Day 10 of pseudopregnancy, rabbits were given an i.v. injection of hCG (10-20 i.u.) that was sufficient to cause new ovulations and the loss of follicular oestradiol secretion. There was an immediate 3-4-fold rise in serum progesterone which returned to near prestimulation values (approximately 27 ng/ml) within 12 h in the presence of an implant containing oestradiol-17 beta. In the absence of oestradiol, serum progesterone continued to decline to reach low values (approximately 4 ng/ml) within 24 h and the original corpora lutea subsequently regressed. The administration of oestradiol 24 h after injection of hCG, when progesterone secretion was low, arrested any further decline in progesterone and then restored serum progesterone to normal values. This steroidogenic effect of oestradiol in vivo was a function of enhanced luteal steroidogenesis; corpora lutea removed and incubated for 12 h produced progesterone at high, linear rates, whereas the corpora lutea from animals that did not receive oestradiol produced low or insignificant quantities of progesterone in vitro. We conclude that hCG at these doses is compatible with continued responsiveness of the corpora lutea to oestrogen and that hCG produces its luteolytic effect primarily by ovulating follicles, thus stopping the secretion of the luteotrophic hormone, oestradiol.

TUMOR NECROSIS FACTOR-α (TNF-α) PRODUCTION AND LOCALIZATION OF MACROPHAGES AND T LYMPHOCYTES IN THE RABBIT CORPUS LUTEUM

“…However, on day 10 of pseudopregnancy, the rabbit was given a second injection of PMSG, followed 2 days later by an injection of hCG to stimulate ovulation and the formation of a second set of corpora lutea. An estradiol implant was placed sc to prevent premature regression of the original corpora lutea as described previously (12). Five days after the second injection of hCG, the ovaries were removed.…”

Hormonal regulation of pregnancy and related behavioral changes in rabbits

“…Lowering the concentration of this hormone in the first trimester of pregnancy leads to the inhibition of embryonic development, which results in the termination of pregnancy (84). Administration of chorionic gonadotropin on the seventh day of mating causes an increase in the number of pregnancy corpus luteum and an increase in progesterone concentration till the 18 th days of pregnancy, which leads to an increase in the fertilization rate (61). It is directly responsible for the increase in estradiol concentration which, as previously mentioned, is an important luteotropic hormone in the rabbit.…”