Ovarian estradiol modulates the stimulatory effect of ovulation-inducing factor (OIF) on pituitary LH secretion in llamas

This study was designed to: 1) characterize the effect of ovulation-inducing factor (OIF) on pituitary LH secretion in ovariectomized (OVX) llamas; and 2) determine the effect of OIF on LH secretion in OVX llamas pretreated with estradiol-17β (E-17β) or estradiol benzoate (EB). In Experiment 1, intact and OVX llamas (n = 5 or 6 per group) were assigned to a two by two factorial design: 1) Intact llamas treated with 1 mL of phosphate buffered saline (PBS); 2) Intact llamas treated with 1 mg of purified OIF; 3) OVX llamas treated with 1 mL of PBS; or 4) OVX llamas treated with 1 mg of purified OIF. In Experiment 2, intact and OVX llamas (n = 5 or 6 per group) were randomly assigned to the following groups: 1) Intact llamas treated with 1 mg of purified OIF; 2) OVX llamas treated with 1.0 mL of PBS; 3) OVX llamas treated with 1.0 mg of purified OIF; 4) OVX llamas primed with E-17β, followed by 1.0 mg of purified OIF. Experiment 3 was similar as described for Experiment 2, except that priming was done with EB. In Experiment 1, animal category by treatment and animal category by treatment by time interactions tended (P = 0.08) to affect LH concentration. The effect of OIF on LH released was partly restored (P < 0.05), to the values observed for the intact OIF-treated females, when OVX llamas were primed with E-17β or BE (Experiments 2 and 3). We concluded that peripheral estradiol concentrations in llamas partially modulates the effect of OIF on pituitary LH secretion; however, other ovarian factor(s) could also participate in this modulatory action.