Evidence for the conservation of biological activity of ovulation-inducing factor in seminal plasma

An ovulation-inducing factor (OIF) in the seminal plasma of llamas and alpacas (induced ovulators) and cattle (spontaneous ovulators) suggests that OIF is a conserved constituent of seminal plasma among mammals. In this study, three experiments were designed to determine the biological effects of OIF in different species. In experiment 1, superstimulated prepubertal female CD-1 mice (n=36 per group) were given a single 0.1 ml i.p. dose of 1) phosphate-buffered saline (PBS), 2) 5 μg gonadotropin-releasing hormone (GNRH), 3) 5 IU hCG, or 4) llama seminal plasma. The proportion of mice that ovulated was similar among groups treated with GNRH, hCG, or seminal plasma, and all were higher than the saline-treated group (P<0.001). In experiment 2, female llamas (n=8 or 9 per group) were intramuscularly treated with 1) 2 ml PBS, 2) 1 ml diluted llama seminal plasma, 3) 3 ml equine seminal plasma, or 4) 3 ml porcine seminal plasma. Experiment 3 was the same as experiment 2 except that the dose of equine and porcine seminal plasma was increased to 8 and 10 ml respectively. All llamas that were treated with llama seminal plasma ovulated and none that were treated with saline ovulated (P<0.0001). The proportion of llamas that ovulated in response to equine and porcine seminal plasma was intermediate. We conclude that the mechanism for the biological response to OIF is present in prepubertal CD-1 mice and that OIF is present in equine and porcine seminal plasma.