Presence of follicular fluid in the porcine oviduct and its contribution to the acrosome reaction

Abstract

Two experiments were conducted to measure the quantity of follicular fluid entering the porcine oviduct following ovulation and to establish its influence on the sperm acrosome reaction in vivo. Prepubertal gilts treated with pregnant mare serum gonadotropin (PMSG) followed by human chorionic gonadotropin (hCG) were used in both experiments. In experiment 1, each of 64 gilts was assigned at random to one of four treatment groups (n = 16 per group): I (preovulatory), surgery 38 hr post-hCG; II (ovulatory), (surgery) 42 hr post-hCG; III (postovulatory), surgery 46 hr post-hCG; IV (ovulation blocked), surgery 46 hr post-hCG but also treated with indomethacin (INDO) at 24 hr. At surgery, both follicular and oviductal fluid were collected for determination of volume and progesterone (P₄) concentration. In experiment 2, sperm were recovered surgically from the uterine horn, isthmus, and ampulla of gilts at 46 hr post-hCG either (1) inseminated and non-INDO-treated controls (n = 5) or (2) inseminated and INDO-treated at 24 hr (n = 4). Using P₄ as a marker, it was calculated that only 0.51% ± 0.10% of the available follicular fluid was present in the oviduct near the time of ovulation and that this amount had decreased 10–12-fold 4 hr later. Mean sperm concentration at 46 hr post-hCG was higher in the uterine horn than in the other two regions (P < 0.05) but the percentage of acrosome-reacted sperm was greater in the ampulla (P < 0.05). The ampullae of ovulating gilts, i.e., containing follicular fluid, had a greater percentage of acrosome-reacted sperm than those in which ovulation was blocked by INDO (P < 0.05). The results of these experiments suggest that only a small amount of follicular fluid reaches the oviduct at ovulation and that this fluid has a stimulatory, but probably nonessential, effect on the acrosome reaction.