The assay of hypertensin from the arterial blood of normotensive and hypertensive human beings

Angiotensin II Studies in Hypertension

1. In primary hypertension, the digital blood vessels are more reactive than normal to angiotensin II as well as to l -norepinephrine.

2. In terms of weight, the potency of angiotensin II in constricting digital blood vessels is 10 times that of norepinephrine in both normotensive and hypertensive subjects.

3. The turnover of angiotensin II-I 131 is slower than normal in patients with primary hypertension.

4. Digital vascular reactivity to both l -norepinephrine and angiotensin II is normal in "pure" renal hypertension.

5. Angiotensin II-I 131 turnover, in contrast, in the case of renal hypertension studied, was slower than in the normal group and was similar to that in the case of primary hypertension.

Angiotensin Skin Tests

The studies reported above indicate that the angiotensin skin test (A.S.T.) is a simple practical measure which has proved of value in differentiating between normotensive and hypertensive individuals. The duration of the blanching of skin by the test differs significantly in normotensives as compared with hypertensives. The test has served as an index [see figure in the PDF file] of differentiation between an emotionally induced elevation of blood pressure and one which may go on to an established hypertensive state. The A.S.T. is a more reliable test in the diagnosis of the latent, labile, or prehypertensive state than is the cold pressor test. Angiotensin-induced hypertension induces a prolongation of the A.S.T. as compared with control periods.

Juxtaglomerular cell counts and human hypertension

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Experimental renal hypertension; mechanism of production and maintenance

The evidence is reviewed that the primary cause of essential hypertension in man is intrarenal obliterative vascular disease, from any cause, usually arterial and arteriolar sclerosis, or any other condition which brings about the same disturbance of intrarenal hemodynamics.

Renal pressor system in hypertension; evidence for circulating hypertensin in chronic renal hypertension; nature and activity of purified hypertensin

Hypertensin has been found in the circulating arterial blood in dogs with experimental renal hypertension and in human beings with essential hypertension. Two different chemical forms of the material have been obtained in purified form and their chemical constitution determined. The decapetide hypertensin I is the initial product of the action of renin on its substrate. This material is transformed to the vasoconstrictor octapeptide hypertensin II by a chloride activated enzyme of the plasma.

The preparation, purification, and amino acid sequence of a polypeptide renin substrate

A purified preparation of a polypeptide renin substrate prepared by tryptic degradation of the protein renin substrate has been analyzed by the fluorodinitrobenzene method and after degradation with renin, carboxypeptidase, and phenylisothiocyanate, has been found to possess the amino acid sequence; asp-arg-val-tyr-ileu-his-pro-phe-his-leu-leu-val-tyr-ser. The first 10 of these amino acids constitutes hypertensin I which is released by cleavage of the leucyl-leucine bond by renin. The remaining 4 amino acids, leu, val, tyr, ser, apparently link hypertensin I to the protein renin substrate.

The amino acid composition of hypertensin II and its biochemical relationship to hypertensin I

Preparations of hypertensin II, obtained from the treatment of hypertensin I by the action of the hypertensin converting enzyme of plasma and purified by countercurrent distribution, were quantitatively analyzed for their amino acid content. Chromatography on ion exchange columns showed the presence of equimolar amounts of aspartic acid, proline, valine, isoleucine, tyrosine, phenylalanine, histidine, and arginine. Hypertensin I was found to contain one mole of leucine and one mole of histidine in addition to the amino acids of hypertensin II. These two amino acids were isolated from the conversion products of hypertensin I and identified as the peptide histidylleucine. Carboxypeptidase digestion of hypertensin I showed the carboxyl terminal sequence of amino acids to be residue-phenylalanyl-histidylleucine. Similar studies of hypertensin II demonstrated residue-phenylalanine. It was concluded that the conversion of hypertensin I by the plasma hypertensin converting enzyme involved hydrolysis of the phenylalanyl-histidine bond to form hypertensin II and histidylleucine. The further removal by carboxypeptidase of phenylalanine from hypertensin II destroyed all of the vasoconstrictor activity.

The amino acid sequence of hypertensin. II

The amino acid sequence of horse hypertensin II has been determined by the use of chymotrypsin, the fluorodinitrobenzene method, and stepwise phenylisothiocyanate degradation. The results indicate that the amino acids of hypertensin II are arranged in the following order: asp-arg-val-tyr-iso-hist-pro-phe.

The purification of hypertensin II

The enzymatic conversion of hypertensin I to hypertensin II is described together with the subsequent purification of the product by means of counter-current distribution. Improved methods are also presented for the preparation of renin and its substrate, as well as in methods for the reaction of these materials and the purification of the resulting hypertensin I.

Reactivity to pressor agents in hypertension

The pressor responses to intravenous injections of angiotonin and s-methyl iso -thiourea have been studied in 50 hypertensive subjects and 20 normotensive controls. The rises of blood pressure in the two groups were similar, being but slightly greater in the hypertensives. After the blood pressure has been reduced with hexamethonium, however, the pressor responses to angiotonin, s-methyl isothiourea and noradrenaline are much greater in hypertensives than normotensive subjects. The responses under these conditions to all three pressor agents run parallel to each other, suggesting that there is no specific increase in reactivity in hypertensive subjects, either to angiotonin or noradrenaline. It has been concluded that there is evidence of increased reactivity to pressor substances in hypertensive subjects but that this is not demonstrable until the blood pressure control mechanisms have been inactivated by hexamethonium.

Amino acid composition and electrophoretic properties of hypertensin I

A preparation of hypertensin I was purified by countercurrent distribution and was shown to migrate as a single component in starch blocks at pH 9.3 and 4.2. It had an isoelectric point of 7.7. Quantitative analysis by ion exchange column chromatography showed eight amino acids in approximately unimolar proportion: aspartic, proline, valine, isoleucine, leucine, tyrosine, phenylalanine, and arginine. There were in addition two moles of histidine.

The purification of hypertensin I

The purification of hypertensin I has been described. The final product which is four times as powerful a pressor agent as l-arterenol, is obtained with an over-all recovery of 40 per cent. The product consists of a single component in countercurrent distribution, having a nitrogen content of 15.97 per cent and a specific activity of 7050 Goldblatt units per mg. of N or 1125 units per mg. of solid. Acid hydrolysis and paper chromatography indicate in a preliminary fashion that there are about nine amino acids present in the intact polypeptide.

The existence of two forms of hypertensin

Two types of hypertensin have been demonstrated by means of counter-current distribution. The first type is the product of the action of the enzyme, renin, upon its substrate and has been designated hypertensin I. It can be rapidly converted to a second approximately equally pressor compound, hypertensin II, apparently through the action of an enzyme in the plasma which requires halide or nitrate for activation. A highly purified preparation containing horse hypertensins I and II caused an elevation of blood pressure when injected into human beings.