STEROID CONTENTS OF AND STEROIDOGENESIS IN-VITRO BY THE DEVELOPING GONAD AND MESONEPHROS AROUND SEXUAL-DIFFERENTIATION IN FETAL SHEEP

The aim of the present study was to establish whether the steroids, pr ogesterone, androstenedione, testosterone and oestradiol, were present in the mesonephricgonadal complex of female and male sheep fetuses ar ound sexual differentiation (that is, from day 28 to day 45 of gestati on, with sexual differentiation occurring at approximately day 32). A second aim was to test whether the mesonephric-gonadal complex, mesone phros (days 35-45 only) and gonad (days 35-45 only) were capable of st eroid synthesis in vitro. The steroid contents in the mesonephric-gona dal complex were not detectable before sexual differentiation. However , from day 35 of gestation onwards, the mesonephric-ovarian complex co ntained mainly oestradiol and the mesonephric-testicular complex conta ined mainly testosterone: from day 35 until day 45 the increase in con tent of these two steroids exceeded the increase in the mass of tissue by more than fivefold. From day 40 to day 45 of gestation, the conten ts of the other steroids in the pathways to oestradiol increased progr essively in both sexes but more in parallel with the increase in tissu e mass. In contrast to the steroid contents in the tissue at recovery, the mesonephric-gonadal tissue from both sexes in tissue culture was able to synthesize most steroids before and after sexual differentiati on and also to metabolise supplementary androstenedione to oestradiol. These findings suggest that many, if not all, of the steroidogenic en zymes in the pathway from cholesterol to oestradiol are present before sexual differentiation. Most of the aforementioned steroids were pres ent in detectable amounts in isolated mesonephros and gonad of both se xes after sexual differentiation. Moreover, for both the isolated meso nephros and gonad, there were increases in the mean contents of most s teroids after culture relative to the contents in the tissues at recov ery. These data suggest that the mesonephros, as well as the gonad, in both sexes is capable of synthesizing steroid. It is concluded that, in the sheep fetus, the female and male gonads are steroidogenically a ctive after sexual differentiation, that the steroidogenic enzymes dev elop before sexual differentiation, and that the mesonephros is a site of steroid synthesis.