SUBSTRATE CONCENTRATION AFFECTS THE IN-VITRO METABOLISM OF 17-HYDROXYPROGESTERONE BY OVARIES OF THE CARP, CYPRINUS-CARPIO

Carp ovarian tissue was incubated with H-3-17-hydroxyprogesterone in t he presence of 0, 0.1, 1, 10, and 100 mu g ml(-1) unlabeled 17-hydroxy progesterone. The pattern of metabolites formed showed a marked variat ion with substrate concentration. Formation of glucuronide and sulphat e conjugates was important only at low substrate concentration. At hig h substrate concentration (10 and 100 mu g ml(-1)) 17,20 alpha-dihydro xy-4-pregnen-3-one was the major metabolite, but at intermediate conce ntrations polar 7 alpha-hydroxypregnane-tetrols predominated. The resu lts support the hypothesis that at low substrate concentrations conjug ating, 5 alpha-reducing and 7 alpha-hydroxylating enzymes, of high act ivity but low capacity, act as scavengers to deactivate any steroids f ormed during the relatively low pituitary gonadotrophin secretions whi ch are necessary for oocyte development, but that during the prespawni ng gonadotrophin surge when high levels of substrate are present these enzymes are saturated and 17,20 alpha-dihydroxy-4-pregnen-3-one (17,2 0 alpha P) becomes the major ovarian steroid. The possible role of 17, 20 alpha P during oocyte final maturation requires further examination .