Circulating Estrogen Levels in the Ram: Influence of Season and Mating, and Their Relationship to Testosterone Levels and Mating Frequency

Seasonal Variation in Circulating Gonadotropin and Testosterone Levels and in Testis Size of Yearling Rams During and Subsequent to Immunoneutralization of Estradiol or Tamoxifen Treatment in the Nonbreeding Season

“…As early as week 2, however, the initial LH response appeared to be blunted (Fig. 4) Sanford et al 1982) and increase in concert with testosterone levels (r:0.88) in late summer and early fall (Sanford et al 1982). In the present study, levels of estradiol in the immunized rams were presumed to have been neutralized effectively in that an excess of antibody-binding capacity was in the circulation throughout the immunization period.…”

“…1981) and gonadal steroid levels in the with acute neutralization where increases in blood circulation (Sanford et al 1977(Sanford et al , 1982 testosterone secretion occur independent of increase. Sertoli cells undergo nuclear hyper-proportionate increases in LH pulsatility.…”

Effects of passive immunization against oestradiol-17 on some endocrine values of the male lamb

“…Although oestradiol implants can suppress plasma levels of LH and FSH in intact (Jenkins & Waites, 1983) and castrated (Schanbacher & Ford, 1977;Alexander & Miller, 1982) sheep, neither in the present study nor that of Land et al (1981) were plasma LH or FSH concentrations significantly affected by removal of endogenous oestrogens. Whilst removal of negative feedback by immunization might be expected to increase the production of both oestradiol and androgens (Nieschlag & Wickings, 1978), the titre of antibody achieved in this study by passive immunization was capable of binding at least 132 times the circu¬ lating oestradiol concentration in male sheep (Sandford et al, 1982). The oestradiol binding capacity in EAB-treated animals, was therefore unlikely to be saturated.…”

“…Manipulation of circulating oestradiol concentrations by steroid implantation (Jenkins & Waites, 1983) or by immunization (Land, Baird & Carr, 1981) has provided evidence for a physiological role for oestrogens in the developing male lamb. Oestradiol implants induced a suppression of the secretion of LH and FSH in intact male lambs (Jenkins & Waites, 1983) and in castrated rams (Schanbacher & Ford, 1977;Alexander & Miller, 1982), although normal endogenous con¬ centrations of oestradiol-17ß are < 15 pg/ml in adult rams (Sandford, Simaraks, Palmer & Howland, 1982). Active immunization against oestradiol resulted in elevated circulating concen¬ trations of testosterone and LH in male rats (Nishihara & Takahashi, 1983) and in adult rams (Schanbacher, 1984) whereas no significant changes in plasma LH or FSH values were observed in male lambs passively immunized against oestradiol or oestrone (Land et ai, 1981).…”