Plasma concentrations of luteinizing hormone, follicle-stimulating hormone and progesterone during the breeding season in ewes immunized against androstenedione or testosterone.

Levels of plasma LH, FSH and progesterone during the breeding season were measured by radioimmunoassay in control ewes and ewes actively immunized against androstenedione-11 alpha-hemisuccinyl--bovine serum albumin or testosterone-3(O-carboxymethyl)oxime--bovine serum albumin. Immunization against androstenedione resulted in normal oestrous cycles with raised plasma LH and progesterone levels and a reduction in the concentration of FSH during the luteal phase. It is tentatively suggested that androstenedione, or its metabolites, could modify the oestrogenic control of LH secretion and facilitate the release of FSH in the ewe. Immunization against testosterone prevented oestrus and resulted in markedly increased levels of LH without alteration of the FSH concentration. Since evidence of increased binding of oestradiol-17 beta was found in the ewes immunized against testosterone, these results cannot be attributed solely to a reduction in the biologically active faction of testosterone.