Effect of Vertebral Artery Infusions of Oxytocin on Plasma Vasopressin Concentration, Plasma Renin Activity, Blood Pressure and Heart Rate and Their Responses to Hemorrhage

Abstract

Infusion of oxytocin into one vertebral artery of anesthetized dogs did not alter plasma vasopressin concentration, blood pressure or heart rate. However, there was a significant (p < 0.01) increase in plasma renin activity (PRA; Δ = 7.6 ± 2.3 ng/ml · h). A 35% hemorrhage caused blood pressure to fall by 9.4 ± 4.0 mmHg (p < 0.01) and PRA to rise by 8.8 ± 2.7 ng/ml · h (p < 0.05). In 8 dogs that were subjected to a similar hemorrhage and that also received an intravertebral infusion of oxytocin, blood pressure was maintained and PRA increased by 14 + 4.3 ng/ml · h (p < 0.05). Heart rate and plasma vasopressin responses were similar in both hemorrhage groups. The results indicate that oxytocin prevented the fall in blood pressure associated with a hemorrhage, possibly by increasing renin release.