Different angiotensin II-forming pathways in human and rat vascular tissues

We studied the angiotensin II-forming pathways in extracts from human and rat vascular tissues. In the extract from human artery, angiotensin I mainly converted to two products, angiotensin-(1-9) and angiotensin II, while in the extract from rat artery, the major angiotensin I products were angiotensin II and angiotensin-(5-10). The concentrations of angiotensin II and angiotensin-(1-9) generated in the human extract (1 mg protein/ml) after incubation for 30 min were 3.2 and 2.5 nmol, respectively, and that of angiotensin II and angiotensin-(5-10) generated in the rat extract (1 mg protein/ml) were 0.28 and 2.3 nmol, respectively. In the extract from human vascular tissues, the angiotensin II formation was inhibited by 8% with lisinopril and by 95% with chymostatin. The other product, angiotensin-(1-9) was inhibited completely by carboxypeptidase inhibitor. In the extract from rat vascular tissues, the angiotensin II formation was suppressed to 4% by lisinopril, but not by chymostatin. The angiotensin-(5-10) formation was completely inhibited by chymostatin. These findings suggest clearly that human vascular tissues contain two angiotensin II-forming enzymes, angiotensin-converting enzyme and chymase, but rat vascular tissues have no chymase-dependent angiotensin II-forming pathway.