Comparison of blood pressure responses to intra-arterial and intra-venous injections of angiotensin I, angiotensin II and bradykinin.

Because of the reported uneven vascular distribution of the enzyme, angiotensin converting enzyme (ACE), we hypothesized that the magnitude of blood pressure responses to bolus injections of angiotensin I (Ang I) and bradykinin (BK) would be dependent upon the route of administration, i.e., intra-arterial (i.a.) or intra-venous (i.v.). Anesthetized rats with cannulas in the left carotid artery and the right internal jugular vein were given bolus injections of each agent, alternating between the two cannulas. Intra-venous injections of Ang I produced transient increases in arterial pressure that were significantly greater (27 +/- 12%) and longer (7 +/- 7%) than those induced by equimolar i.a. injections within the same preparation. Intra-venous injections of BK produced transient decreases in arterial pressure that were significantly smaller (72 +/- 4%) and shorter (78 +/- 11%) than similar i.a. injections. Unexpectedly, i.v. injections of Ang II also evoked slightly larger transient increases in arterial pressure (11 +/- 4%) than similar i.a. injections. These results suggest that enzymatic alterations of Ang I and BK probably by angiotensin converting enzyme during their initial passage through the pulmonary circulation has a small but significant influence on their pressor effects.