Ram lambs need FSH for normal testicular growth, Sertoli cell numbers and onset of spermatogenesis

The effect of FSH on the development of the testis in the ram lamb was exam ined in two experiments where lambs were passively immunized against ovine beta-FSH from birth until 100 or 160 d. In both experiments, immunization r esulted in a slower testicular growth relative to that of controls. This ef fect became apparent at around the start of the period of rapid testicular growth (60-70 d of age) and resulted in testicular weights at the end of tr eatment ranging from 37 to 51 % of those of control groups. Within the test is, this was reflected in shorter seminiferous tubules (48-64 % of controls ) and in lower numbers of Sertoli cells per testis (57-82 %). In the rams i mmunized until 160 d of age, spermatogenesis had begun and immunization aga inst FSH provoked a lower production of germinal cells which was not solely due to the lower number of Sertoli cells but also due to fewer germinal ce lls bring supported by each Sertoli cell. However, the numbers of A(0) sper matogonia per testis and the daily production of the A(1) spermatogonia wer e unaffected by immunization, but the production of the B-2 spermatogonia a nd, as a consequence, of leptotene and pachytene spermatocytes and of round spermatids were all markedly lower (43-47 % of controls). These effects we re not due to any decreases in the secretion of LH or testosterone as seen in the blood levels of these two hormones. These results show that, in the ram lamb, FSH is essential for normal testicular development and for the es tablishment of a normal population of Sertoli cells. They also confirm that , once spermatogenesis is established, FSH is necessary for a normal produc tion of germinal cells, with one or m*ore of the divisions between the A(1) and B-2 spermatogonia being sensitive to suppression of FSH. (C) Inra/Else vier, Paris.