Variations in Pituitary and Blood Lh During Puberty in the Male Lamb. Relation to Time of Birth

Testicular weight, pituitary LH concentration, blood plasma LH were measured in Ile-de- France lambs born in the sexual season (September) or out of season (February) to see how these characters are modified at puberty.During the period of low testicular growth, the impuberal period, there was a large increase in pituitary LH concentration and a significant linear increase in blood plasma LH ; the half- life of the latter is the same as in the adult.In the period of rapid testicular growth, the prepubertal and pubertal period, pituitary LH stabilised or decreased according to the season, and blood LH remained at a level lower than that of the peak reached at the end of the preceeding period.Thus spermatogenesis commenced after blood LH reached peak values.In the lamb, a species in which spermatogenesis starts two to three months after birth (WATS ON , Sn P S>•ox D and M C CANCE, i9j6 ; CouxoT, r 9 62 ; SKINNER et al., 19 68) it has been demonstrated that the impuberal testis is dependent upon pitui- tary hormones and especially upon I!H since hypophysectomy induces testicular weight regression while I,H reverses the effects of this operation (C OUROT , 1970 ).Thus, it is of interest to know the evolution of the pituitary content and that of the blood plasma levels of this hormone in the lamb during a period including the esta- blishment of spermatogenesis.Such results are reported in the present paper.As the sheep has a well defined sexual season, the work dealt with lambs born either at the end of February or September.