Renin and angiotensin. A survey of some aspects

Relation of plasma to interstitial fluid volume in essential hypertension

Extracellular water (radiobromine), plasma volume (radioiodinated human serum albumin), and peripheral plasma renin activity were measured simultaneously in men with uncomplicated, untreated essential hypertension and in normal subjects. The ratio of plasma volume to interstitial fluid volume (PV/IF) was significantly lower in hypertensive patients (0.194 vs. 0.223, P <0.001). This could not be explained only on the basis of the diminished plasma volume found in hypertensive patients (17.3 ml/cm of body height vs. 18.7 ml/cm, P <0.05), as three normal subjects with marked plasma volume contraction had normal PV/IF ratios (0.224). This disturbed ratio in hypertensives suggests, therefore, an abnormality in the mechanism regulating the distribution of extracellular water in essential hypertension. Peripheral plasma renin activity correlated inversely with plasma volume, but not with extracellular water volume, suggesting that these two indices of body fluid volume are not always functionally interchangeable.

Renin-aldosterone system in Parkinson's disease

Low blood pressure is frequent in the akinetic form of Parkinson's disease. A low renin activity in plasma as well as a low rate of aldosterone secretion is demonstrated in these patients. Renin activity in the plasma is further decreased by treatment with L-dihy-droxyphenylalanine, thus partially accouinting for the hypotensive episodes seen with this form of therapy.

Arterial pressure responses to discontinuing antihypertensive drugs

A wide spectrum of arterial pressure responses to discontinuing long-term antihypertensive drug treatment was found in 65 patients. In five, spontaneous pressure variations prevented judging effects of drug discontinuance. Of the remaining 60, pressure returned to pretreatment levels in 21, and rose toward control levels in 37; while in two, diastolic hypertension did not reappear in more than 8 years. Rate of rise of arterial pressure seemed related to type of hypertension and to height of diastolic pressure and severity of vascular disease before treatment. In six of nine patients who had had malignant hypertension and six of nine with renal arterial disease, pressure rose promptly and treatment was restarted within a month. Among essential hypertensive patients, those who remained off treatment for 2 to 6 months had significantly lower pretreatment pressure than those whose hypertension returned in less than 2 months. The two whose diastolic hypertension seemed "cured" had no distinguishing features.

These results suggest that most hypertensive patients require continuous treatment for good pressure control; downward resetting of pressure by treatment is rare.

Plasma renin in chronic experimental heart failure and during renal sodium "escape" from mineralocorticoids

A striking increase in the plasma renin level occurred in dogs with low output right heart failure secondary to tricuspid insufficiency and pulmonic stenosis and in three of five animals with high output failure produced by a large arteriovenous fistula. When dogs with a small arteriovenous fistula were given daily injections of DOCA, the renal sodium "escape" phenomenon occurred. In these animals, the level of plasma renin was suppressed during DOCA administration both during the initial period of sodium retention and also later when sodium balance was normal or negative. In contrast, when dogs with a larger arteriovenous fistula but without evidence of cardiac failure were given DOCA, they retained sodium and developed signs of congestive heart failure. However, in these animals with congestion and ascites, in contrast to the dogs that developed spontaneous high output failure, the plasma renin was low. Renin-substrate was unaltered in all of the experimental situations studied except for the decrease observed in dogs with low output right heart failure. In these animals, it seems likely that decreased renin-substrate was secondary to hepatic congestion and liver damage. The renin-angiotensin system does not seem to be related to the "escape" phenomenon, and renin does not appear to be the factor that makes the kidney unusually responsive to mineralocorticoids. Thus, in experimental heart failure the renin-angiotensin system was activated, but in the congestive syndrome produced by DOCA the plasma renin level was suppressed.

Aldosterone production and juxtaglomerular granules

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