Angiotensin converting enzyme in the endothelium and smooth muscle cum adventitia of the normo- and hypertensive rat aorta.

Angiotensin converting enzyme (ACE) activity in the endothelium and smooth muscle cum adventitia of the normo- and hypertensive rat aorta was investigated. The aortic tissues of spontaneously hypertensive (SHR) rats, compared to those of the Wistar Kyoto (WKY) and Sprague Dawley (SD), contained significantly higher level of ACE activity. Expressed as mumole per min per mg total protein, the endothelium of the SHR contained 105 +/- 11 (mean +/- SEM) and those of the WKY and SD, 69 +/- 7 and 77 +/- 9, respectively. Similarly, the ACE activity in the smooth muscle cum adventitia were 97.6 +/- 8.2, 52.6 +/- 6.4 and 25.7 +/- 4.1 for the SHR, WKY and SD respectively. These results support our earlier assumption that the high level of ACE activity in the lung of SHR is a reflection of the increase in ACE activity of the blood vessels. However, our results and related findings of other investigators do not permit firm speculation as to whether the increase in ACE activity in the SHR is the cause or the result of hypertension in these animals.