The Formation of Oestrogens by the Autotransplanted Ovary of the Ewe Perfused in Vivo With C19 Steroids

Abstract

The autotransplanted ovary of the ewe was perfused in vivo via the ovarian artery with either 14C or 3H labelled C19 steroids. 17β-Oestradiol was the major phenolic steroid isolated in ovarian venous blood from either testosterone or androstenedione. Smaller amounts of oestrone were obtained but there was no 17α-oestradiol, oestriol nor conjugated oestrogens isolated. The yield of oestrogen was approximately ten fold greater from androstenedione than from testosterone suggesting that the main route of oestrogen biosynthesis in the ovine ovary is via the former steroid. The effect of infusing luteinizing hormone (LH) at the rate of 10 μg per hour on the conversion of androstenedione to 17β-oestradiol was measured in 5 experiments. In 2 experiments, when the steady state was not achieved, the increasing rate of conversion was halted. On the other hand LH resulted in a temporary increase followed by a decrease in the rate of conversion in the remaining 3 experiments in which there was a constant rate of conversion in the control samples. These results are compatible with the concept that LH stimulates the aromatisation of androstenedione to oestrogens by the ovary in vivo.

Relationship between LH receptor concentrations in thecal and granulosa cells and in-vivo and in-vitro steroid secretion by ovine follicles during the preovulatory period

“…Both testosterone (Moor, 1977;Hay & Moor, 1978;Scaramuzzi, Baird, Clarke, Martensz & Van Look, 1980;Webb & England, 1982) and androstenedione have been suggested as major precursors for oestradiol production (Rado et al, 1970). In the present study, incubation of follicles with 250 ng testosterone/ml failed to alter in-vitro oestradiol production in all except Group 2 non-ovulatory follicles (Text- fig.…”

“…Paradoxically, the administration of high doses of LH in the sheep inhibits oestradiol secretion both in vivo and in vitro (Rado, McCracken & Baird, 1970;Moor, 1974) and elicits a similar response in the rat (Hori, Ide & Miyake, 1969;Hori, Ide, Kato & Miyake, 1970). The mechanisms whereby LH enhances or inhibits follicular oestradiol secretion are not well understood; however, the presence of large concentrations of LH receptors in the membrana granulosa of the major oestradiol-secreting follicle (England et al, 1981b;Webb & England, 1982) fig.…”

Plasma Concentrations of Ovarian Hormones During the Oestrous Cycle of the Sheep and Cow

“…2) or in the studies of Shemesh & Hansel (1974). The role of testosterone is not clear; it is an ovarian hormone which is a precursor of oestradiol (Rado, McCracken & Baird, 1970) but it may also be involved in the triggering mechanism for the onset of luteolysis in ruminants.…”

Functional and Structural Relationships in the Graafian Follicle Population of the Sheep Ovary

“…; oestrone accounts for only about 10% of the total oestrogen output (Moore et al, 1969). No detectable oestradiol-17a, oestriol or conjugated oestrogen is produced during the cycle in this species (Rado et al, 1970). The production of androgen by the ovaries of sheep parallels the production of oestrogen (Baird et al, 1968).…”