TIME AND LOCATION OF THE ACROSOME REACTION DURING SPERM TRANSPORT IN THE FEMALE RABBIT

Motile spermatozoa with lifted or absent acrosomal caps (“reacted acrosomes”) were observed by phase contrast microscopy exclusively in the oviduct of the rabbit reproductive tract during the first 16 hours post coitum (p.c.). They were first identified at six hours p.c. in flushings from the lower isthmus of the oviduct and were present in both the lower and upper isthmus two hours later. Motile spermatozoa with reacted acrosomes appeared in the lower ampulla (the site of fertilization) at ten hours p.c. Such spermatozoa were obtained from all regions of the oviduct at 12 and 16 hours p.c. but they always constituted a minority of the freely swimming spermatozoa recovered. The percentage of spermatozoa with activated motility was higher following the acrosome reaction, and their apparent swimming speeds were lower than those of intact spermatozoa. The role of ovulation in the induction of acrosome reactions was studied in females artificially inseminated per vaginam (AI), with or without the induction of ovulation, and in females mated either two hours before or two hours after ovulation. The proportion of motile spermatozoa with reacted acrosomes in the isthmus and ampulla of non‐ovulatory females 12 hours after AI was similar to their proportions in these regions 12 hours after mating or 12 hours after AI with induced ovulation. Four hours after delayed matings, i.e., two or six hours after ovulation, motile spermatozoa were confined to the tubal isthmus and none had undergone the acrosome reaction. These findings indicate that the products of ovulation and the endocrine changes associated with ovulation in the rabbit need not be directly involved in the induction of the acrosome reaction in vivo. Copyright © 1979 Wiley‐Liss, Inc., A Wiley Company