Follicle Diameter and Systemic Hormone Interrelationships during Induction of Follicle Collapse with Intrafollicular Prostaglandin E2 and F2 in Mares

摘要

Contents The objectives were to determine: (i) whether intrafollicular administration of PGE2 and PGF2 to mares would hasten follicle collapse and (ii) the differences in reproductive hormone characteristics in mares with spontaneous and prostaglandin-induced follicle collapses. Six mares were followed for two oestrous cycles each: when the mares reached a follicle diameter of 30-35mm and showed mild-to-moderate endometrial oedema, mares were administered a single 0.5ml dose containing 500g PGE2 and 125g PGF2 (treatment cycle) or a placebo (0.5ml of water for injection; control cycle) into the preovulatory follicle (Hour 0). Blood samples were collected, and serial ultrasound examinations were performed until follicle collapse. Treated mares showed follicle collapse significantly earlier (20.0 +/- 5.9h) than the control mares (72.0 +/- 10.7h). The LH, progesterone, total oestrogens and oestradiol concentrations did not differ between groups; however, the progesterone concentration increased more between 48 and 72h after follicle injection in the treatment compared to the control cycles (P0.05). In conclusion, intrafollicular treatment with PGE2 and PGF2 hastened follicle collapse in mares without the simultaneous use of an inductor of ovulation; despite the early induction of follicle collapse, the profiles of LH and oestradiol were not altered. This study provides information on the role of prostaglandins (PGs) in the process of follicle wall rupture and collapse and suggests that this may happen even before the beginning of the sharp rise in circulating LH at the final stage of the ovulatory surge.