Ovarian blood flow throughout the estrous cycle and early pregnancy in sows

The association between ovarian arterial blood flow (OBF), as measured with electromagnetic blood-flow transducers, and the concentrations of progesterone, estrone and estradiol-17 beta in systemic blood were determined throughout the estrous cycle and the first 21 days of pregnancy in four sows (first day of estrus or mating=Day 0). Changes in OBF were positively correlated (P less than 0.01) with the concentrations of progesterone in systemic blood throughout the estrous cycle (requal+0.63) and early pregnancy (requal+0.65) and negatively correlated (P less than 0.01) with estrone (r=-0.53) and estradiol-17 beta (r=-0.51) during the estrous cycle, but not (P greater than 0.10) during early pregnancy. In nonpregnant sows, OBF was lowest at estrus, highest during the luteal phase, and declined precipitously after Day 14 in association with declining concentrations of progesterone and increasing concentrations of estrogens in systemic blood. Patterns of OBF and progesterone during the subsequent pregnancy of each sow were similar to those observed during the estrous cycle until Day 12. Between Days 12 and 15 of pregnancy, blood flow to the ovary and progesterone in systemic blood exhibited transient rises of 26% (P less than 0.01) and 20% (P less than 0.05), respectively. Both an ovarian vasodilatory and luteotropic effect of the conceptuses was demonstrated on days critical for maintenance of the corpora lutea during early pregnancy in this species.