SECRETION OF TRANSFERRIN IN OVINE SEMINIFEROUS TUBULE CELL-CULTURES IN RESPONSE TO FSH - INFLUENCE OF BREED, SEASON OF BIRTH AND AGE OF LAMBS

The response of lamb Sertoli cells to follicle stimulating hormone (FS H) was investigated by measuring transferrin secretion in seminiferous tubule cell cultures throughout the non-pubertal and the prepubertal periods. Cells could be cultured from birth until they attained a test icular weight of 19 g. The characteristics of individual dose-response curves were compared according to the breed, season of birth and test icular weight of the lambs. At the same season of birth and within a g iven testis weight range, dose-response curves of Romanov and Ile-de-F rance lambs were similar. Within a given testis weight range, spring-b orn animals exhibited a higher maximal transferrin secretion than autu mn-born lambs, but the ED50 was similar. The main factor of variation of the dose-response curve parameters was the testicular weight of the lambs: the amplitude of FSH response increased 3-fold from a testicul ar weight of 6 g onwards, i.e. from the appearance of spermatogonia in seminiferous tubules. The ED50 increased 5-fold from 11 g onwards, i. e. from the beginning of the prepubertal period. Thus, Sertoli cells b ecome less sensitive to FSH as spermatogenesis develops in seminiferou s tubules. This phenomenon is largely the result of higher phosphodies terase activity and is greatly reduced by 1-methyl-3-isobutylxanthine (MIX).