A STUDY OF THE EFFECTS OF PITRESSIN AND SEROTONIN IN THE MAINTENANCE OF BLOOD PRESSURE IN THE HYPOPHYSECTOMIZED HYPOTHERMIC RAT

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Abstract
It was shown previously that warming the exteriorized kidneys, along with the infusion of Pitressin in hypophysectomized cooled rats, gave excellent maintenance of blood pressure at low body temperatures. Infusions of saline perfusates of kidney and heart into hypophysectomized cooled rats were ineffective by themselves but, combined with the infusion of Pitressin, gave good maintenance of blood pressure at low body temperatures. Since some clotting may have occurred in blood remaining in the organs when the isolated organs were perfused it was necessary to test the effectiveness of an agent released during clotting, namely, serotonin. By itself serotonin had no effect on blood pressure in hypothermic hypophysectomized rats down to a body temperature of 20 °C, at which temperature it had a striking pressor action. When Pitressin and serotonin were infused together, the blood pressure was well maintained in hypophysectomized cooled rats down to a body temperature of 16 °C. These experiments indicate the importance of Pitressin, and the interaction of Pitressin with other factors, in maintaining blood pressure in hypothermic animals.