Prostacyclin effect on heart rate in the pig.

The purpose of this study was to assess the hemodynamic response after prostacyclin infusion into the venous system and into the carotid artery in the pig. During the study the following circulatory variables were studied: mean systemic arterial pressure, mean pulmonary arterial pressure, wedge pressure, heart rate, cardiac output, systolic and diastolic left ventricular pressure, stroke volume, total systemic resistance, total pulmonary resistance, left ventricular stroke work. Our results confirm that prostacyclin is a powerful hypotensive agent. The hypotensive effect seems to be due to a peripheral vasodilatation of arterial and venous vessels. Venous infusion caused only 19% tachycardia, as opposed to 36% caused by arterial infusion for the same percentage of blood pressure reduction. This suggests that prostacyclin probably stimulates cardiopulmonary vagal receptors. The effect of prostacyclin on heart rate, therefore, may be twofold and in opposite directions: one action causing tachycardia secondary to hypotension, and the other inviting bradycardia through direct vagal stimulation.