The Effects of Oxytocin on the Pulmonary and Systemic Circulation in Pregnant Ewes

Abstract

The haemodynamic effects of oxytocin on the pulmonary and systemic circulation were studied in six awake, pregnant (> 140 days gestation) ewes. Bolus doses of oxytocin 0.2 units/kg and then 0.8 units/kg were administered. A dose of 0.2 units/kg resulted in small but significant increases in mean pulmonary artery pressure (14%, P < 0.05) and pulmonary vascular resistance (24%, P < 0.05. A bolus of 0.8 units/kg resulted in a significant increase in mean arterial pressure (20%, P < 0.05) and systemic vascular resistance (33%, P < 0.05). Acute pulmonary hypertension was then induced with glass bead microemboli (150–200 μm), with an increase in pulmonary artery pressure of 26 mmHg and pulmonary vascular resistance of 448 dyn. s. cm−5. Boluses of oxytocin 0.2 and 0.8 units/kg were then administered. There were no significant changes, except for a 30% increase in systemic vascular resistance at one minute after oxytocin, 0.8 units/kg (P < 0.05).