Cholesterol and phospholipid concentrations and phospholipase activity were measured in fluid from cannulae collected from the bovine oviductal 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 μg ml⁻¹ over all stages) than in ampullary oviductal fluid (164.5 ± 11.3 μg ml⁻¹), and maximal concentrations (284.5 ± 25.5 μg ml⁻¹) were found during the luteal stage (serum progesterone concentration ≥ 1.5 ng ml⁻¹). The concentrations of the phospholipids sphingomyelin and lysophosphatidylcholine increased 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 (12.1 ± 2.7% of total phospholipids) than in fluid collected near oestrus and ovulation (7.5 ± 1.5% and 6.9 ± 1%, respectively). The concentration of lysophosphatidylcholine was greater (P < 0.01) in ampullary (19.2 ± 1.6% of total phospholipids) than in isthmic oviductal fluid (9.9 ± 1.1%) collected near ovulation. The ratio of cholesterol to total phospholipid was highest in oviductal fluid collected from the isthmus during all stages (2.3 μg ml⁻¹:% total phospholipid), while the minimal ratio was found in ampullary fluid collected near ovulation (1.5). Phospholipase activity was higher (P = 0.03) in isthmic oviductal fluid (20.4 ± 3.2% product formed) than in ampullary oviductal 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 temporal differences in the concentrations of lipids in oviductal fluid provide general support for the concept that the isthmus serves as a sperm reservoir, while the ampulla is the site of the bovine sperm acrosome reaction.

Summary. The oviducts of 4 cows were cannulated and oviduct fluid was collected daily from the exteriorized cannulas for a total of 5 oestrous cycles. Daily serum samples were assayed for oestradiol-17β and progesterone to monitor the oestrous cycle. Data for each cycle were compared for oviduct fluid collected during the non-luteal phase (serum progesterone ⩽ 1·5 ng/ml) and the luteal phase (serum progesterone > 1·5 ng/ml). During the non-luteal phase oviduct fluid volume was higher and the osmolality was lower than during the luteal phase. Total protein, cholesterol and phospholipid secreted daily was greater during the non-luteal phase. Cholesterol and protein concentrations were generally lower during the non-luteal phase, but phospholipid concentrations were generally higher. About 40% of the phospholipid in oviduct fluid was phosphatidylcholine and lysophosphatidylcholine, while phosphatidylinositol and lysophosphatidylinositol accounted for 20%. The ratio of 1-acyl-phospholipid to diacylphospholipid increased during the non-luteal phase. An increased cholesterol to phospholipid ratio, and a decreased cholesterol to protein ratio in oviduct fluid also were associated with the non-luteal phase. Changes in the lipid composition of oviduct fluid during the oestrous cycle may play a role in the preparation of gametes for fertilization.

Keywords: oviduct fluid; cow; phospholipid; cholesterol; protein