Periovulatory changes in ovarian temperature in ewes.

Thermistors were implanted in intact ewes, and ovarian and aorta temperatures were recorded for 72 hours, following the removal of a progesterone implant intended to induce estrus. Serum levels of luteinizing hormone (LH) were measured hourly over a 10 hour period beginning at the onset of estrus. Ovaries were examined by laparotomy at the end of each experiment. Estrus behavior, LH surge, and a fresh corpus luteum were all found to be present in four, and absent in two, of a total of six experiments. To remove variations in basal body temperature, ovarian temperatures were measured relative to aorta temperature at all times. In the nonovulating ewes, both mean ovarian temperatures varied at random, whereas in the ovulating ewes they decreased by approximately 0.15 degrees C. to reach a minimum 1 hour before the time of maximum rate of increase in LH. The ovulating ovaries differed from the contralateral ovaries (where ovulation did not occur) in two respects: the mean temperature in the ovulating ovaries was lower by 0.02 to 0.10 degrees C. at all times, and its preovulatory decrease began several hours earlier. When taken in conjunction with published data on secretion and on the local and systemic effect of estradiol, these findings, are consistent with the hypothesis that ovarian estradiol induces an increase in ovarian blood flow. A heat-sink effect of the uterine mass due to its proximity to the ovaries may also be involved.