Local exchange of oxytocin from the ovarian vein to ovarian arteries in sheep.

Abstract

Local transfer of 125I-labeled oxytocin from the ovarian vein to arteries supplying the ovary, the oviduct, and the tip of the uterine born has been investigated. In five sheep, 10 infusions of 125I-oxytocin over a period of 1 h were performed, and the concentration of labeled polypeptide in the peripheral plasma was compared to ovarian arterial plasma. During 2 consecutive infusions into each animal's ovarian vein, blood was collected simultaneously from the following sites: ovarian branch of the ovarian artery (OBOA), tubal branch of the ovarian artery (TBOA), uterine branch of the ovarian artery (UBOA), and from the jugular vein. In all experiments the concentration of 125I-oxytocin in ovarian arterial plasma was higher than in peripheral plasma. The ratio of ovarian artery/jugular vein for 125I-oxytocin was: OBOA 2.8, TBOA 1.8, UBOA 1.6. Based on a 4 ml/min blood flow through ovarian arteries supplying ovary, oviduct, and the tip of the uterine horn, the local transfer of the total amount of oxytocin infused was estimated to be about 1% (range: 0.1-4.4%). Analysis of variance did not reveal significant differences in the exchange ratios between OBOA, TBOA, and OBOA. However, the variances within these groups are significant, presumably because of anatomical variation in the degree of surface contact area between arteries and veins at the ovarian pedicle. It is concluded that polypeptides are locally recirculated to ovaries, oviduct, and the tip of the uterine horn in a higher concentration than is supplied by peripheral blood. This could provide a mechanism for local distribution and concentration of the ovarian peptides that regulate reproductive function.