RAM SPERMATOZOA COCULTURED WITH EPITHELIAL-CELL MONOLAYERS - AN IN-VITRO MODEL FOR THE STUDY OF CAPACITATION AND THE ACROSOME REACTION

The effects of different epithelial cells, namely, hamster oviduct, sh eep oviduct, and pig kidney epithelial cells (IBRS-2), on the viabilit y, percentage of progressive motility (PPM), and acrosome reactions of ejaculated ram spermatozoa were investigated. Sperm aliquots were cul tured on cells, cell-conditioned medium 199, or control medium 199. Th e PPM of unattached spermatozoa was estimated after 0, 3, 6, 9, 12, an d 24 hr of incubation at 37-degrees-C under 5% CO2 in air. Viability a nd the occurrence of true acrosome reactions were assessed using a tri ple-stain technique. Spermatozoa started to attach within 1 hr of cocu lture with the hamster or sheep oviductal epithelial cell (OEC) monola yers, and these spermatozoa showed vigorous tail motion. No spermatozo a were found to attach to the IBRS-2 monolayer. The PPM of unattached spermatozoa cocultured with the various types of epithelial cell monol ayers for 12 hr was significantly higher than that of spermatozoa incu bated in conditioned media or medium 199 alone (54% in hamster OEC vs. 40% in conditioned; 68% in sheep OEC vs. 38% in conditioned; 36% in c ontrol medium). On the other hand, after 24 hr of incubation, there we re no differences in the PPM of spermatozoa cocultured with epithelial cells or incubated in conditioned media. The percentages of cells und ergoing a true acrosome reaction reached maximum values (P < 0.05) in spermatozoa incubated for 9 hr in the presence of hamster OEC (22.5%) or for 12 hr on sheep OEC (20.5%) monolayers. IBRS-2, a commercial non reproductive cell type, had a positive influence on both PPM and sperm viability but no effect on the occurrence of the acrosome reaction. I nteractions leading to the acrosome reaction were thus observed only w hen spermatozoa were cocultured with OEC monolayers. The values of PPM in unattached sperm cells seen after 12 hr of coculture with OEC or I BRS-2 were still at a high level (52-67%) for in vitro fertilization. The coculture with OECs provides an ''in vitro'' model to study the ca pacitation processes in a situation that may resemble that occurring i n vivo. Moreover, the coculture with hamster OECs may provide a conven ient and standardized in vitro system to study mechanisms underlying c apacitation and the acrosome reaction. (C) 1993 Wiley-Liss, Inc.