Increases in testosterone secretion in adult rams with immunoneutralization of endogenous estradiol occur in the absence of increases in pulsatile LH release or testicular LH receptors.

The testes of the ram become more responsive to LH stimulation following immunoneutralization of endogenous estradiol. The possibility that testosterone secretion is facilitated by increased LH-binding activity in the testes was investigated in the present study conducted with adult Dorset X Leicester X Suffolk rams during the time of testicular recrudescence. Patterns of episodic LH release and testosterone secretion (days--5, 10 and 24) and LH-binding activity in testicular biopsy samples (days--1, 14 and 28) were assessed on the days indicated relative to the onset of passive immunization and the establishment of relatively low titres (approximately 1:200) of estradiol antiserum. During the experimental period, mean serum testosterone concentration increased by approximately 150% for the immunized rams as basal concentration and pulse amplitude increased, while all characteristics of testosterone secretion remained unchanged for the nonimmunized rams. Characteristics of LH release and the concentration of LH-binding sites in the testes, however, were always similar for both groups of rams. Further, group differences in FSH and PRL secretion and in the concentration of testicular FSH-binding sites did not occur. These results provide evidence for an estradiol direct (gonadotropin independent) negative-feedback component in the regulation of Leydig cell function in the ram.