Conversion of progesterone to 5 alpha- and 5 beta-reduced metabolites in the hen and its potential role in the induction of the preovulatory release of luteinizing hormone.

In the laying hen, progesterone was shown to be converted in vitro in the pituitary gland and the hypothalamus to 5 beta-pregnane-3,20-dione (5 beta-pregnane-3 alpha-ol-20-one (5 beta,3 alpha-ol) and 5 alpha-pregnane-3,20-dione (5 alpha-DHP) and in the hyperstriatum dorsale to 5 beta-DHP and 5 beta,3 alpha-ol. The conversion of progesterone to 5 beta-reduced metabolites was greater in the hyperstriatum dorsale than in the hypothalamus (P < 0.001) and greater in the hypothalamus than in the pituitary gland (P < 0.01). The conversion of progesterone to 5 beta-reduced metabolites was greater than its conversion to 5 alpha-DHP in the pituitary gland (P < 0.01) and the hypothalamus (P < 0.001). The possibility was investigated that 5 alpha-DHP and 5 beta-DHP may act as metabolic intermediaries in the mechanism by which progesterone exerts a positive feedback effect on LH release. Progesterone, 5 alpha-DHP and 5 beta-DHP were injected into laying hens at doses of 0.05, 0.25 and 1.25 mg/kg and the changes in the concentration of plasma LH were followed for 4 h thereafter. Secretion of LH was stimulated after treatment with progesterone or 5 alpha-DHP but not 5 beta-DHP. Progesterone stimulated Lh release more effectively than did 5 alpha-DHP, since an increase in the concentration of plasma LH was observed after 0.25 mg progesterone/kg but not after the same dose of 5 alpha-DHP. It was concluded that in the hen 5 alpa-DHP is unlikely to play a role in the induction of the preovulatory release of LH.