SYNTHESIS AND REGULATION OF 17-ALPHA-HYDROXY-20-BETA-DIHYDROPROGESTERONE IN IMMATURE MALES OF ONCORHYNCHUS-MYKISS

Three experimental approaches were chosen to study the question if the progestin 17 alpha-hydroxy-20 beta-dihydroprogesterone (17 alpha 20 beta OHP) is synthesised in testes of young Oncorhynchus mykiss, in which the absence of spermatozoa was verified histologically: first, in order to detect 20 beta-hydroxysteroid dehydrogenase activity (20 beta HSD), testes homogenates were incubated with H-3-labeled 17 alpha OHP. Metabolites were analysed by TLC, HPLC, and repeated crystallization to constant isotope ratios. One of the metabolites was identified as 17 alpha 20 beta OHP-H-3, indicating that already immature testes contain 20 beta HSD activity and are able to produce 20 beta-reduced steroids. Second, 17 alpha 20 beta OHP was quantified by radioimmunoassay in incubates of testes fragments. The sensitivity of the gonads to gonadotropin II (GtH II) became evident when comparing incubations in the absence and presence of GtH II. Third, plasma levels of 17 alpha 20 beta OHP were significantly higher in animals injected with partially purified salmon gonadotropin, compared to controls. Thus, for the first time, it could be shown that 20 beta HSD is present in testicular cells other than spermatozoa. Furthermore, 17 alpha 20 beta OHP is indeed secreted at a very early stage of testicular development; 17 alpha 20 beta OHP secretion is also responsive to GtH II. Future studies will have to show if the functions of this progestin include the stimulation of spermatogenesis.