Flow of blood to the ovaries of ewes throughout the estrous cycle.

Abstract

A Doppler ultrasonic blood flow procedure was evaluated to determine if it could be adapted for use on vessels as small (I.D. ≅ 0.5 mm) as the ovarian artery in sheep. When blood was pumped through silastic tubing (I.D. = 0.38 and 0.57 mm) the values calculated for blood flow using the Doppler procedure were highly correlated (P<0.01) with the known flow rates. A second experiment was conducted to compare the Doppler ultrasonic procedure for measuring blood flow to the ovaries of ewes and the uptake of radioactive microspheres. Although it was not possible to measure blood flow directly (ml/min) with the radioactive microsphere method, when the cpm/g of ovarian tissue were compared to the ml/min blood flow calculated using the Doppler procedure, there was a high degree of correlation (r = 0.94, P<0.01). These results suggested that the Doppler ultrasonic procedure was reliable for the quantification of blood flow to the ovaries of ewes. In a final experiment the flow of blood to the ovaries of four ewes was quantified throughout an estrous cycle. Blood samples for hormone analysis and blood flow data were collected at 2–6 h intervals. Significant correlations were noted between serum levels of LH and FSH (P<0.05), LH and prolactin (P<0.05), and FSH and prolactin (P<0.01). Systemic levels of progesterone and blood flow to the ovary bearing the corpus luteum were also correlated (P<0.05). Blood flow to the luteal ovary increased from approximately 0.7 ml/min during the estrual phase of the cycle to 3 to 5 ml/min during the mid-luteal phase. This observation suggests that the amounts of LH and prolactin, as well as other substances, such as oxygen, glucose, cholesterol, etc., which reach the corpus luteum were increased. This mechanism probably plays a very important role in supporting the increased function of the corpus luteum during the mid-luteal phase of the estrous cycle.