A preovulatory temperature gradient between the isthmus and ampulla of pig oviducts during the phase of sperm storage.

Fine thermistor probes positioned in each end of the same oviduct and connected to the same scale were used to measure temperature gradients in the lumen before and after spontaneous ovulation in normally-cyclic gilts. Readings were taken after full surgical closure of a mid-ventral incision and a subsequent period of stabilization, but whilst animals remained under general anaesthesia. A small but consistent difference in temperature was recorded between the proximal ampulla and distal isthmus of the same oviduct in each of 20 preovulatory gilts. In 10 of these animals that had not mated, the isthmus was a mean of 0.43 degree C cooler than the ampulla (range 0.2-0.7 degree C) whereas in 10 mated animals the isthmus was 0.69 degree C cooler (range 0.2-1.6 degree C); 3 animals in the latter group had within-oviduct differences of greater than or equal to 1 degrees C. By contrast, in 12 animals that had recently ovulated, the isthmus was a mean of only 0.1 degree C cooler than the ampulla; there was no measurable temperature gradient in 3 of the animals, whilst the isthmus was 0.1 degree C warmer in 2 animals. The preovulatory temperature differences are thought primarily to reflect the extent and activity of the vascular and lymphatic beds in the oviduct tissues and, together with specific chemical microenvironments, may facilitate the relatively prolonged period of sperm storage in the distal portion of the isthmus.