Further Investigations on the Mechanism of Oestrone Production in the Ovary

Abstract

Following the injection of chorionic gonadotrophin into immature female rats, oestrogen is produced in the ovary and passes into the circulation between the 26th and 27th hour after the injection. This has been shown in two experiments. First, if the injected rat is ovariectomized before the 26th hour, oestrus is inhibited, but if the ovaries are only removed 27 hr. after the gonadotrophin injection oestrus occurs normally [Zondek, 1940]. The time involved has been confirmed by experiments [Zondek, 1940; Zondek, Sulman & Sklow, 1941] in which antigonadotrophin has been injected into immature female rats at various times after injecting chorionic gonadotrophin. If the antihormone is given up to 26 hr. after the chorionic gonadotrophin the normal reactions of the rats (oestrus and the appearance of`b lood-points' and corpora lutea in the ovaries) are partially or completely inhibited, while if the antihormone is given 27 hr. after the gonadotrophin there is no inhibition.It is possible that the oestrogen is produced in the ovary solely in the 26th hour after the injection but it is also possible that the interval between the gonadotrophin injection and the passage of the oestrogen into the circulation is occupied by the formation of an oestrogenically inactive precursor ('pro-oestrogen') in the ovaries. The experiment recorded below has been devised to test these points.An injection of chorionic gonadotrophin into immature female rats has been followed 18 hr. later by the injection of sufficient antigonadotrophin to neutralize the response of the rats. This antihormone has been followed in its turn by a second gonadotrophin injection, 20 hr. after the first. If the oestrogen produced is formed in the ovaries only in the single hour 26 hr. after the injection of gonadotrophin, the oestrous response of the rats should occur 20 hr. later than it would after the single gonadotrophin injection. If, however, pro-oestrogen is already present in the ovary when the antihormone is injected this may be transformed into oestrogen under the influence of the second gonadotrophin injection so that the oestrous response should not be delayed. This is actually what happens.

Oestrogen Synthesis in Vitro by Ovaries From Rats in Different Phases of the Oestrous Cycle

“…Another possible explanation is that cells in the vaginal smear do not reflect ovarian steroid synthesis prevailing at the precise time of the observations. Zondek (1940) and Zondek & Sklow (1942) suggest that oestrogen causing early vaginal cornification in the rat is elaborated in the 26 hr. preceding evidence of vaginal cornification.…”