APPEARANCE AND LOCALIZATION OF DELTA5-3BETA-HYDROXYSTEROID DEHYDROGENASES AND 17BETA-HYDROXYSTEROID DEHYDROGENASES INQUAIL AND CHICK EMBRYO GONADS (COTURNIX COTURNIX JAPONICA) HISTOENZYMOLOGICAL STUDY AND COMPARISON WITH CHICKEN GONADS (GALLUS GALLUS DOMESTICUS)

1. 1. In the embryonic gonads, the Δ5-3β-HSDH has been detected in the primary cords as early as 4 1 2 days for the quail, 6 1 2 days for the chick. The activity of the embryonic ovary is more pronounced than that of the testis; the activity in the chick testis appears sooner than in the quail. 2. 2. In the ovary, the Δ5-3β-HSDH is confined to cell clusters of the medullary cords giving rise to the interstitial cells, which later are distributed in the stroma and theca externa. These clusters get conspicuous, early in the chick (8 day's embryo), tardily in the quail (13 day's embryo). A 17β-HSDH is also present in the ovarian epithelium, at the end of the embryonic development and its localization does not interfere with that of the Δ5-3β-HSDH. 3. 3. In the testis, the Δ5-3β-HSDH is appearing gradually in three different sites. The initial reaction in the cord cells, present before sexual differentiation lasts during embryonic development but fades away some time after hatching. The enzymatic reaction of the interstitial tissue and of some cells in the cords may indicate a functional specialization of these cells which begins earlier in the chick (8 1 2 day embryo) than in the quail (13 1 2 day embryo). The Δ5-3β-HSDH activity which characterizes the interstitial cells of the adult testis, is also found in these cells in the advanced chick embryo and in the quail after hatching. 4. 4. The observations described above in the birds are compared with those reported for other Vertebrates. © 1969.