ACE IN 3-TUNICAE OF RAT AORTA - EXPRESSION IN SMOOTH-MUSCLE AND EFFECT OF RENOVASCULAR HYPERTENSION

Angiotensin I-converting enzyme (ACE) is known to be present at the su rface of endothelial cells and also in the adventitia in large vessels . The presence of ACE in the vascular smooth muscle remains controvers ial. We microdissected segments of adventitia and media with or withou t endothelium from a region devoid: of collateral arteries. The membra ne-bound ACE activity in the media averaged 41% (pmol [glycine-1-C-14] hippuryl-L-histidyl-L-leucine hydrolyzed.g tissue(-1).min(-1)) of the values found in the whole aorta, whereas the adventitia contained only 6%. Immunoreactive ACE in media was characterized by Western blotting . ACE mRNAs were detected and characterized after polymerase chain amp lification in isolated media. Angiotensin I and angiotensin II were eq ually able to contract medial rings, and the response to angiotensin I was blocked by enalaprilat. In aortas of two-kidney, one-clip hyperte nsive rats, there was an increase in ACE mRNA estimated by ribonucleas e protection assay (P = 0.02) and in ACE activity at 15 days and 1 and 3 mo after clipping. This corresponded to a 1.5- to 2-fold increase i n the ACE activity of both the media and the adventitia compared with sham-operated rats (P less than or equal to 0.02). Thus ACE gene expre ssion occurs in smooth muscle of rat aorta, which contains roughly the same amount of enzyme as the endothehum and readily converts angioten sin I to angiotensin II. ACE in the medial layer and the adventitia is upregulated in renovascular hypertension.