Contents In many vertebrates, females store sperm received at mating in specialized reservoirs until fertilization. In some species, sperm are routinely stored for up to a decade. But the structures used to store sperm vary considerably across taxa, suggesting the underlying mechanisms might be equally variable. In mammals, after mating, sperm pass through the utero‐tubal junction and bind to epithelial cells of the oviduct isthmus to form a reservoir. This reservoir regulates sperm function, including viability and capacitation, ultimately affecting sperm lifespan. In addition, sperm binding to oviduct cells influences oviduct cell gene transcription and translation, perhaps to aid sperm storage and fertility. The sperm reservoir allows successful reproduction in species in which semen deposition and ovulation are not always synchronized. The focus of this review is on recent studies of the functions of oviduct fluid and of the adhesion molecules that allow sperm to adhere to the oviduct epithelium. The important of glycans on the oviduct epithelium is highlighted.

Heparin specifically and saturably binds to bovine spermatozoa and stimulates capacitation as assessed by the ability of spermatozoa to undergo a zona pellucida-induced acrosome reaction (AR) in vitro. However, the structural features of heparin important for capacitation are poorly understood. The purpose of this study was to determine the importance of the sulfate content of heparin for its potency to bind to bull spermatozoa and promote agglutination and capacitation. The pyridine salt of heparin was N-desulfated, which reduced its mean sulfate content from 19.7% to 11.6%. The N-desulfated heparin was then resulfated by incubation with trimethylamine sulfur trioxide for 6, 12, or 24 hr, raising sulfate to original concentrations. Heparin but not N-desulfated heparin competed with [3H]-heparin to bind to spermatozoa. Heparin at 11.6 micrograms/ml reduced [3H]-heparin binding by half when competing with a saturating concentration of the radiolabeled compound (12 micrograms/ml). N-desulfated heparin did not displace [3H]-heparin. Heparin, resulfated 6 hr or 12 hr, was equal to native heparin in binding potency. Heparin at 50, 100, or 250 micrograms/ml caused more than 40% of the cells to head-to-head agglutinate in aggregates of 8 or more. N-desulfated heparin did not cause agglutination. After spermatozoa were incubated with 0, 5, 10, 50, 100, or 250 micrograms/ml of heparin for 4 hr, 100 micrograms/ml of lysophosphatidylcholine (LPC)-induced AR within 20 min in 21.3, 37.7, 27.8, 45.3, 54.2, or 42.5% of the cells, respectively. Sperm exposed to the same concentrations of N-desulfated heparin exhibited AR of 17.7, 27.3, 24.3, 22.5, 27.7, or 33.8%, respectively, following exposure to LPC. Resulfated heparin did not agglutinate or capacitate spermatozoa. In conclusion, N-desulfation of heparin abolished heparin's ability to bind to, agglutinate, and capacitate bovine spermatozoa. Resulfation of N-desulfated heparin restored binding activity but not agglutination or capacitation activity.