Cation concentrations in fluid from the oviduct ampulla and isthmus of cows during the estrous cycle.

To detect variations in oviduct fluid cation concentrations, Ca++, Mg++, K+, and Na+ were determined for daily samples of blood serum and bovine oviduct fluid collected from indwelling isthmic and ampullary catheters. Isthmic oviduct fluid Ca++ concentration was significantly greater than that in ampullary fluid, particularly around estrus and ovulation. Maximum Ca++ concentrations found in isthmic oviduct fluid at estrus (2.57 +/- .22 mM) and at ovulation (2.50 +/- .29 mM) were similar to those of medium used for in vitro capacitation of bovine sperm. Concentrations of Mg++ in oviduct fluid differed significantly by estrous cycle stage, but not by oviduct region, and were consistently lower than those detected in serum. No relationships were found for K+ or Na+ with respect to region or stage, but K+ was generally higher in oviduct fluid than in serum. The concentration of K+ averaged over stage and region (4.46 +/- .13 mM) and the K+:Na+ ratio (.032 +/- .002) were similar to those reported in bovine in vitro capacitating and fertilizing media. Concentrations of Ca++ and Na+ from peritoneal fluid from nonstaged cows were similar to those of oviduct fluid or serum. The Mg++ concentration was greater, and K+ concentration was less, in peritoneal than in oviduct fluid.