CHOLESTEROL, PHOSPHOLIPID AND PHOSPHOLIPASE-ACTIVITY OF AMPULLARY ANDISTHMIC FLUID FROM THE BOVINE OVIDUCT

Cholesterol and phospholipid concentrations and phospholipase activity were measured in fluid from cannulae collected from the bovine oviduc tal isthmus and ampulla at different stages of the oestrous cycle. The cholesterol concentration and cholesterol normalized by protein were significantly (P = 0.03) greater in isthmic oviductal fluid (224.3 +/- 42.7 mu g ml(-1) over all stages) than in ampullary oviductal fluid ( 164.5 +/- 11.3 mu g ml(-1)), and maximal concentrations (284.5 +/- 125 .5 mu g ml(-1)) were found during the luteal stage (serum progesterone concentration greater than or equal to 1.5 ng ml(-1)). The concentrat ions of the phospholipids sphingomyelin and lysophosphatidylcholine in creased at different stages of the cycle and in different regions. In the ampulla, the concentration of sphingomyelin was significantly (P < 0.05) greater in oviductal fluid collected during the luteal phase (1 2.1 +/- 2.7% of total phospholipids) than in fluid collected near oest rus and ovulation (7.5 +/- 1.5% and 6.9 +/- 1%, respectively). The con centration of lysophosphatidylcholine was greater (P < 0.01) in ampull ary (19.2 +/- 1.6% of total phospholipids) than in isthmic oviductal f luid (9.9 +/- 1.1%) collected near ovulation. The ratio of cholesterol to total phospholipid was highest in oviductal fluid collected from t he isthmus during all stages (2.3 mu g ml(-1):% total phospholipid), w hile the minimal ratio was found in ampullary fluid collected near ovu lation (1.5). Phospholipase activity was higher (P = 0.03) in isthmic oviductal fluid (20.4 +/- 3.2% product formed) than in ampullary ovidu ctal fluid (14.6 +/- 1.4%); the lowest activity (12.6 +/- 1.7% product formed) was in fluid collected during the phase of the oestrous cycle immediately before ovulation. We conclude that the regional and tempo ral differences in the concentrations of lipids in oviductal fluid pro vide general support for the concept that the isthmus serves as a sper m reservoir, while the ampulla is the site of the bovine sperm acrosom e reaction.