The effect of intravenous infusions of angiotensin and noradrenaline on systolic blood pressure and critical opening pressure of tail vessels in conscious rats.

Abstract

A spectroscopic technique for the measurement of systolic blood pressure and critical opening pressure of tail vessels in conscious rats is described. The values for systolic blood pressure obtained by this indirect technique were compared with those obtained by direct recording from a cannulated carotid artery. The correlation between the two sets of measurements was highly significant and the regression coefficient was very close to unity. In a separate series of experiments the effects of intravenous infusions of angiotensin or noradrenaline on the critical opening pressure of tail vessels were investigated in conscious ganglion-blocked rats. Both drugs produced dose-dependent increases in critical opening pressure and systolic blood pressure. This contrasts with the situation in the human finger where angiotensin has been shown to produce a decrease in critical opening pressure, indicating relaxation of a least some of the vessels in the finger, while at the same time producing an overall increase in digital vascular resistance.