COUNTER CURRENT TRANSFER OF OXYTOCIN FROM THE VENOUS-BLOOD OF THE PERIHYPOPHYSEAL CAVERNOUS SINUS TO THE ARTERIAL BLOOD OF CAROTID RETE SUPPLYING THE HYPOPHYSIS AND BRAIN DEPENDS ON THE PHASE OF THE ESTROUS-CYCLE IN PIGS

The objective of the present study was to determine whether or not the neuropeptide, oxytocin, can move by counter current transfer from ven ous blood of the perihypophyseal cavernous sinus into arterial blood o f the carotid rete supplying the brain and hypophysis, and also whethe r this exchange depends on the day of the estrous cycle. Isolated head s of gilts (n = 37), on different days of the estrous cycle, a ere sup plied with autologous, oxygenated and heated blood at a stable blood f low and pressure through the right carotid artery for 30 min. I-125-Ox ytocin (I-125-OT),, infused into both cavernous sinuses through the an gularis oculi veins for 5 min. After I-125-OT infusion, radiolabeled o xytocin was found in arterial blood taken from the carotid rete in all 7 gilts on Days 1-3, and in 7 of 9 gilts on Days 12-13 of the estrous cycle. In general, the level of radioactivity in arterial blood durin g Days 12-13 was significantly lower (p < 0.002) than during Days 1-3 of the estrous cycle. No I-125-OT was found in arterial blood from Day s 4 through 11 (n = 10) or from Day 14 to the beginning of ovulation ( n = 11). These results provide evidence for the counter current transf er of oxytocin from hypophyseal and brain venous effluent (cavernous s inus) to arterial blood supplying the hypophysis and brain, during the ovulation period and the late luteal phase of the estrous cycle. The meaning of this process is not as yet known and needs further study.