Soluble oviductal factors do enhance capacitation of bull sperm. So, sperm release is brought about by changes within the sperm, although these changes could be initiated by signals from the oviduct. buy flovent inhaler
Sperm binding to oviductal epithelium appears to involve carbohydrate recognition. The first evidence for this came from our studies with fetuin and its terminal sugar sialic acid, which were found to inhibit binding of hamster sperm to the epithelium. Colloidal gold-labeled fetuin bound to the heads of fresh epididymal hamster sperm but not to sperm that had been incubated under capacitating conditions until they became hyperactivated. Fetuin also bound to certain glycoprotein bands on Western blots of membrane extracts from fresh hamster sperm, and the bands were reduced in extracts from sperm incubated under capacitating conditions.
These data indicate that there is a lectin on the heads of uncapacitated hamster sperm that binds fetuin and is responsible for attachment of sperm to the epithelium. We also investigated binding of stallion sperm to epithelium and found that asialofetuin and its terminal sugar, galactose, blocked sperm binding. Dob-rinski and coworkers were able to isolate a galactose-binding protein from the plasma membrane of stallion sperm using galactose affinity chromatography. In cattle, bull sperm binding to oviductal epithelium was determined to be specifically blocked by fucose. Pretreatment of epithelium with fucosidase, but not galactosidase, reduced binding (Fig. 2).
FIG. 2. Fucose inhibits bull sperm binding to explants of oviductal epithelium taken from estrous heifers. A) Glycoproteins and polysaccharides expressing a variety of terminal sugar residues were tested for the capacity to competitively inhibit binding of bull sperm to oviductal explants. Only fucoidan, which is composed of fucose and fucose-sulfate, significantly reduced the density of bound sperm, c, Sperm-TALP control; fc, fucoidan; ft, fetuin; af, asialofetuin; ov, ovalbumin. Mean ± SEM sperm/0.1 mm2 of epithelium, n = 5 replicates. Density of sperm binding did not differ between isthmic and ampullar epithelium, p > 0.05. **Fucoidan reduced binding, p < 0.001. B) Next, fucose was tested at various doses for its capacity to inhibit bull sperm binding to explants, and it did so in a dose-dependent manner. Mean ± SEM sperm/0.1 mm2 of oviductal epithelium; n = 5 replicates. C) Finally, explants pretreated with 0.1 U/ml fucosidase for 5 h at 39°C bound significantly fewer sperm than those pretreated with fucosidase plus its specific inhibitor, deoxyfuconojirimycin, or with 5 U/ml galactosidase. c, Sperm-TALP control; f, fucosidase; f+i, fucosidase + inhibitor; g, galactosidase. Mean ± SEM sperm/0.1 mm2 of epithelium; n = 3 replicates. Density of sperm binding did not differ between isthmic and ampullar epithelium, p > 0.05. **Fucosidase pretreatment reducing sperm binding, p < 0.001. Adapted from Lefebvre et al., Biol Reprod 1997; 56,1200-1201, Figures 1, 3, and 4.