Intramuscular injections of male pheromone 5 alpha-androstenol change the secretory ovarian function in gilts during sexual maturation.

In addition to the standard olfactory pathway typical for signaling pheromones, the existence of a humoral pathway for the priming action of pheromones has been earlier postulated. In this study in vivo experiment was performed to establish whether intramuscular injections of boar pheromone, 5 alpha-androstenol (5 alpha-androst-16-en-3-ol), might change the development and secretory function of the ovarian follicles during sexual maturation of gilts. Gilts from groups I (n=15) and II (n=13) received androstenol (10 microg/gilt/injection; i.m.) three times a week from day 192 to 234 of age. Similar, control gilts (group C; n=13) received saline. Additionally, the nasal cavity of animals from group II was irrigated with zinc sulfate solution to depress olfactory function. The reproductive organs and follicular fluid were collected on day 240 of age. There were no significant differences among groups concerning the weight of the ovary and uterus, the length of the uterine horns and intensity of cytochrome P450(scc) and P450(arom) immunoexpression. However, gilts treated with boar pheromone had a higher (p<0.01) total number of follicles > 3 mm in diameter and a lower index of atresia. In addition, androstenol-treated animals were characterized by higher concentrations of progesterone (the 1-3 mm and 3-6 mm follicles; p<0.01 and 0.001, respectively) and estradiol (follicles 3-6 mm; p<0.001) than those of controls. The results of the present study demonstrate that intramuscular injections of androstenol stimulate the development and secretory function of the ovarian follicles in gilts during sexual maturation. They also support the hypothesis that androstenol, as a priming boar pheromone, may influence reproductive processes in female pigs acting as a chemical signal via humoral pathway.