The polyol pathway in the bovine oviduct

The oviducts likely provide optimized micro-environments for the final maturation of gametes, fertilization, and early embryo development. Hexoses, including glucose, fructose, and sorbitol, are involved in these critical reproductive events. Monosaccharide production is controlled, in part, by the polyol pathway and requires two enzymes: an aldose reductase (AR) that reduces glucose into sorbitol, followed by its oxidation into fructose by sorbitol dehydrogenase (SDH). We analyzed the expression of AR and SDH in the isthmus and ampulla of the bovine oviduct at the proliferative, mid-luteal, and late-luteal phases of the estrous cycle by quantitative PCR and immunoblots. Immunochemistry and an assay of SDH activity were also performed. The quantity of hexoses in whole sections of isthmus and ampulla were determined by liquid chromatography coupled to mass spectrometry. In sum, AR expression was restricted to the isthmus, while SDH was mostly expressed in the isthmic-ampullary junction and the ampulla, specifically concentrated in the luminal epithelium of the oviduct. The estrous cycle had no impact on protein expression of AR and SDH. Instead, the levels of AR and SDH expression were associated with higher ratios of sorbitol to fructose in the isthmus (1.6) than in the ampulla (4.1; P = 0.005). These results are discussed in light of physiological events occurring in the oviduct.