THE BIOLOGY OF MAMMALIAN SPERMATOZOA IN THE OVIDUcr A DISSERTATION SUBMITTED TO THE GRADUATE DMSION OF THE UNIVERSITY OF HAWAII IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PlITLOSOPHY IN BIOMEDICAL SCIENCES

The oviduct occupies a unique position in mammalian reproduction as the site of sperm transport, the final maturation of sperm and egg, fertilization, and the initial development of the embryo. This dissertation examines the factors that control the number, distribution and physiological state of spermatozoa in the oviduct. The golden hamster (Mesocricetus auratus) was used as the animal model. The following summarizes my findings. The uterotubal junction restricts the passage of homologous and heterologous spermatozoa into the oviduct, furthermore, sperm motility is essential for efficient passage. After mating, spermatozoa rapidly enter the oviductal isthmus where they are stored. When mating occurs shortly after the onset of estrus, spermatozoa are stored for at least 8 h until near the time of ovulation. When mating occurs during ovulation, spermatozoa are stored for a minimum of 3 h. Spermatozoa stored in the isthmus during the preovulatory period do not become fully capacitated until near the time of ovulation. When mating occurs during ovulation, spermatozoa require a minimum of 3 h in the isthmus to become fully capacitated. Although many thousands of spermatozoa are stored in the isthmus, only a relatively small percentage of these spermatozoa survive. The spermatozoa that do survive attach to the oviductal mucosa during storage. Later, due to physiological changes in the sperm head plasma membrane that accompany capacitation, a small number of these spermatozoa detach from the mucosa and ascend to the ampulla to fertilize the eggs.