PLASMA-CONCENTRATIONS OF LUTEINIZING-HORMONE AND FOLLICLE-STIMULATING-HORMONE DURING ANESTRUS IN EWES ACTIVELY IMMUNIZED AGAINST OESTRADIOL-17-BETA, ESTRONE OR TESTOSTERONE

The concentrations of LH and FSH in jugular venous plasma were measured during anoestrus in control ewes and ewes actively immunized against 17β-oestradiol-6-(O-carboxymethyl)oxime-bovine serum albumin, oestrone-6-(O-carboxymethyl)oxime-bovine serum albumin or testosterone-3-(O-carboxymethyl)oxime-bovine serum albumin. During a 12h sampling period, the basal level of LH and the frequency of LH pulses were significantly increased in all the immunized animals. The plasma FSH concentration was increased in two out of the oestradiol-immunized ewes and two out of three oestrone-immunized animals. The plasma FSH concentration in the testosterone-immunized animals was similar to the control values. Significant titres of antibodies to oestradiol-17β were found in all the immunized animals. It is suggested that binding of oestradiol-17β in the circulation by antibodies reduced the negative feedback action normally exerted by this steriod on LH secretion and, to a lesser extent, on FSH secretion. However, since the oestradiol antibody titres in the testosterone-immunized and oestrone-immunized ewes were considerably lower than those found in the oestradiol-immunized animals, it is possible that testosterone and oestrone, perhaps by acting as prehormones, could influence the negative feedback control by oestradiol-17β of gonadotrophin secretion in the anoestrous ewe.