Estradiol-17β secretion by the newly formed corpus luteum of a macropodid marsupial, the quokka ( Setonix brachyurus)

Abstract

The production of significant amounts of estradiol-17β from the 2-day-old corpus luteum of the macropodid marsupial, Setonix brachyurus (quokka), was shown using an in vitro perifusion system. Sliced corpora lutea and finely chopped extra-luteal ovarian tissue (cortex plus interstitial tissue) were perifused separately for 2 hr, in tandem for the next hour (with the perifusate from the ovarian tissue directed into the chamber containing the corpora lutea), and separately again for a further 2 hr. Overall production rates of estradiol measured by radioimmunoassay were 1.0 pg (mg hr) −1 from luteal tissue and 0.64 pg (mg hr) −1 from the extra-luteal tissue. Androgen production rates were 0.18 ng (mg hr) −1 and 0.06 ng (mg hr) −1 from luteal and extra-luteal tissues, respectively, and progesterone was produced at a rate of 0.80 ng (mg hr) −1 from luteal tissue and 16.5 pg (mg hr) −1 from extra-luteal tissue. Production rates of all three steroids from the perifused tissue increased significantly when the ovary and corpus luteum were perifused in tandem. The secretion of C19 and C18 steroids from the young corpus luteum suggests that luteinization is not yet complete at this stage in the reproductive cycle of the quokka, and the tissue would be better described as a “postovulatory follicle”. This is supported in the literature by the occurrence of mitoses in granulosa cells for 6–7 days after resumption of the delayed cycle. This delayed maturation of the macropodid corpus luteum, which is associated with the secretion of significant quantities of estradiol and only a transient spike of progesterone, is discussed in relation to the longer cycles and gestation periods characteristic of macropodid marsupials.