The Metabolism of Angiotensin II

The half-lives of angiotensin II, angiotensin II-amide, angiotensin III, Sar1-Ala8-angiotensin II and renin in the circulatory system of the rat

1. Methods are described for estimating the half-life of angiotensin analogues and renin in the rat, from the time course of the blood pressure changes they evoke. 2. The following half-life values were measured: angiotensin II, 16 +/- 1 sec; angiotensin III, 14 +/- 1 sec; angiotensin II-amide, 15 +/- 1 sec; Sar1-Ala8-angiotensin II, 6.4 +/- 0.6 min; renin, 3.0 +/- 0.4 min. The distribution volume of angiotensin was found to be 18 ml./kg body wt. 3. It is inferred that the Asp1 residue does not reduce the rate of angiotensin II catabolism, but that substitution of this residue by sarcosine may inhibit catabolism while substitution by asparagine has no effect. 4. Five experimental criteria were identified which indicate that these methods give reliable estimates of the half-life. It is suggested that these results are more accurate than most previous half-life estimates. 5 When tachyphylaxis to angiotensin II-amide occurs, the pressor activity of the plasma is not reduced.

Paroxysmal hypertension in aortitis syndrome

Three patients with aortitis syndrome ehibited paroxysmal hypertension which seemed to result from baroreceptor dysfunction. All of the patients had signs of active inflammation of aortitis syndrome and stenotic carotid and subclavian arteries. During the attacks, the blood pressure rose to at least 230 mm. Hg systolic and the heart rate exceeded 100. However, with prolonged administration of steroid hormones, the attacks ceased. In two patients with dilated thoracic aortas and aortic regurgitation, the attacks of paroxysmal hypertension occurred without apparent precipitating factors and were followed by anginal pain with marked ST depression. The sympathicotonic state resulting from the disturbance of the baroreceptors was considered to be responsible for the attacks. In another patient, the attacks occurred in the course of treatment with a steroid hormone and were provoked only by voluntary micturition. This post-micturition hypertension was presumed to be an expression of abnormal overshooting following a fall in blood pressure after voiding.