Quail embryos with a sex-linked eye pigmentation marker allowing sex identification at autopsy provided a biological model for radioimmunoassay of sex steroids in embryonic quail gonads at a very early stage (51/2 and 61/2 days). The purpose was to demonstrate a sex difference in hormonal potentialities of the gonads before any morphological indication of sexual differentiation. Evidence of early steroidogenesis by undifferentiated gonads could be obtained: estrogen synthesis characterized female gonads, while testosterone was produced by the gonads of both sexes. The sex hormonal production was concomitant with, or even preceded, the apparent beginning of sex differentiation of gonads.

An early treatment of quail eggs with an antiestrogen (Tamoxifen = TAM) modifies the female gonads morphologically. In the left ovary, the proliferation of the germinal epithelium and formation of a cortex is markedly inhibited, while the medulla on both sides becomes more developed and keeps a cordal organization. The effects of TAM on the hormonal potentialities of 15-day embryo gonads have been investigated by radioimmunoassay. The data have been compared with those of normal gonads. The results indicate that the TAM treatment does not mainly modify the hormonal levels and patterns in the gonads of both sexes and does not inhibit the function of the hypothalamo-hypophyseal-gonadal axis. The reduced cortical development is thus not linked to an estrogen decrease but to competitive effects on receptors at the level of this tissue.

In vitro effects of factors such as testosterone or hCG on steroidogenesis by 12-day quail embryo gonads have been investigated by radioimmunoassays. The purpose was to compare the hormonal potentialities (estradiol, estrone, and dihydrotestosterone; E1, E2, DHT) of normal and diethylstilbestrol-treated gonads. The results demonstrate that the reduced steroid production by the treated ovaries does not result from their inability to respond to both factors, but reflects their weakened stimulation in vivo at the time of explantation. On the other hand, the secreting abilities of the DES-treated male gonads do not greatly differ from those of normal testes; even in the presence of favorable factors, and despite their feminization, the ovotestes are effectively unable to produce significative amounts of estradiol. These results are compared with others obtained elsewhere in quail and in chick embryos.

This report describes the fine structure of the "wheel" cells and of epithelial structures which both characterize the interstitial tissue of hypophysectomized and intact senescent rats. The regressive changes induced in normal ovarian interstitial cells of 25-26 day-old hypophysectomized rats were studied from 7 days to 15 months after the operation. They mainly consist in a rapid cytoplasmic dedifferentiation of these steroidogenic cells which, by one month after hypophysectomy, could be only identified by their specific nuclear pattern ("wheel" cells). Further changes of their organelles are only quantitative. These interstitial cells become perennial cells with no ultrastructural signs of senescence. In one year-old animals, the presence of both epithelial testis-like tubes and epithelial cellular cords provides evidence that these structures represent two different morphological arrangements for a similar cellular aspect. Unlike established "wheel" cells, these epithelial structures are evolutive and the thickening of their basement membrane can be considered as an age criterion. The follicular origin of the testis-like tubes and the complex formation of the cords are discussed in the light of our previous photonic study and compared with similar structures occurring in the senile rat ovary and in other situations.

Early treatment of Quail eggs by tamoxifen produces a striking inhibition on normal differentiation of the female gonads. This anti-estrogen restricts cortical proliferation in the ovary while it favours the development of the medulla of both gonads. As a result their morphology and organization diverge toward a more neutral or even testicular pattern. Since tamoxifen is able to compete with the endogenous estrogens, these results underline their role in female differentiation of the Quail gonads.

Agenesis of the mesonephros was obtained by preventing its early induction by the Wolffian duct. In the older embryos (14 to 19 days) studied, the ovaries differentiated in the absence of the underlying mesonephros, but were reduced in size. Their different cell populations (somatic and germinal) were however present and showed typical cytological features. Nevertheless, both components of the ovary, the medulla and the cortex, demonstrated lack of harmonious development. The medulla contained much larger lacunae; the cortex was shrunken with less secondary cords. At these stages, the gonocytes are not yet in premeiosis. These results are discussed in relation to the role of the mesonephros in gonadogenesis and in initiation of meiosis.

In vitro steroid production by quail gonads of control and of diethylstilbestrol (DES)-treated embryos (10 and 14 days) has been investigated by radioimmunoassay. The data indicate that, during normal development, ovaries produce mainly estradiol (E2) estrone (E1) and testes, testosterone (T). The androgen reaches similar levels in both sexes, but the TE1 + E2 ratio is always higher for testes than for ovaries; this is also the case for the right rudimentary female gonads which have limited aromatizing capacities. Steroidogenesis is initially restricted mainly to the Δ 5-pathway; Δ 4-ketosteroids appear only toward the end of incubation. The feminization of the male embryo by DES does not enhance estrogen formation by ovotestes. This is also the case for the DES-treated ovaries in which estrogen production is significantly inhibited at both ages. This occurs in the treated gonads of both sexes, despite continued production of T which is considered a good estrogen precursor. These results are compared with those obtained in chick, and they are discussed in the context of the factors involved in sex differentiation.

We have previously studied the steroidogenesis in chick embryonic gonads, according to age, sex and side, by association of organotypic culture and radioimmunoassay. We present now a similar study with 10 and 14 day quail embryonic gonads for comparison with chick gonads of corresponding stages of development. The total steroid production (sum of seven steroids assayed) is less important in quail than in chick gonads. At 10 days, we note in quail, as opposed to the chick, a total deficiency of 4ene-androstenedione production in both sexes, and of progesterone mainly in male. The only steroids synthesized are estrogens (E1, E2) chiefly in left female gonad. At 14 days, the production of some steroids as progesterone, 4ene-androstenedione, DHA and testosterone appears to be higher than at 10 days. The formation of progesterone and 4ene-androstenedione by gonads of both sexes demonstrates the presence of Δ5-3β HSD at this later stage of development.

In quails, H-Y antigen is induced by oestrogens in the gonads of the originally H-Y negative homogametic sex but not in non-gonadal tissues. This is consistent with the view that oestrogens act via H-Y antigen in the organization of the avian gonad.