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

Arterial blood sampling in male CD-1 and C57BL/6J mice with 1% isoflurane is similar to awake mice

Isoflurane (ISO) is a commonly used anesthetic that offers rapid recovery for laboratory animal research. Initial studies indicated no difference in arterial Pco₂ (PaCO2) or pH between conscious (NO ISO) and 1% ISO-exposed CD-1 mice. Our laboratory investigated whether arterial blood sampling with 1% ISO is a suitable alternative to NO ISO sampling for monitoring ventilation in a commonly studied mouse strain. We hypothesized similar blood chemistry, breathing patterns, and cardiovascular responses with NO ISO and 1% ISO. C57BL/6J mice underwent unrestrained barometric plethysmography to quantify the pattern of breathing. Mice exposed to hypoxic and hypercapnic gas under 1% ISO displayed blunted responses; with air, there were no breathing differences. Blood pressure and heart rate were not different between NO ISO and 1% ISO-exposed mice breathing air. Oxygen saturation was not different between groups receiving 2% ISO, 1% ISO, or air. Breathing frequency stabilized at ~11 min of 1% ISO following 2% ISO exposure, suggesting that 11 min is the optimal time for a sample in C57BL/6J mice. Blood samples at 1% ISO and NO ISO revealed no differences in blood pH and PaCO2 in C57BL/6J mice. Overall, this method reveals similar arterial blood sampling values in awake and 1% ISO CD-1 and C57BL/6J mice exposed to air. Although this protocol may be appropriate in other mouse strains when a conscious sample is not feasible, caution is warranted first to identify breathing frequency responses at 1% ISO to tailor the protocol.

NEW & NOTEWORTHY Conscious arterial blood sampling is influenced by extraneous factors and is a challenging method due to the small size of mice. Through a series of experiments, we show that arterial blood sampling with 1% isoflurane (ISO) is an alternative to awake sampling in C57BL/6J and CD-1 male mice breathing air. Monitoring breathing frequency during 1% ISO is important to the protocol and should be closely followed to confirm adequate recovery after the catheter implantation.

Translational success stories: angiotensin receptor 1 antagonists in heart failure

The title of the proposed series of reviews is Translational Success Stories. The definition of "translation" according to Webster is, "an act, process, or instance of translating as a rendering of one language into another." In the context of this inaugural review, it is the translation of Tigerstedt's and Bergman's(1) discovery in 1898 of the vasoconstrictive effects of an extract of rabbit kidney to the treatment of heart failure. As recounted by Marks and Maxwell,(2) their discovery was heavily influenced by the original experiments of the French physiologist Brown-Séquard, who was the author of the doctrine that "many organs dispense substances into the blood which are not ordinary waste products, but have specific functions." They were also influenced by Bright's(3) original observation that linked kidney disease with hypertension with the observation that patients dying with contracted kidneys often exhibited a hard, full pulse and cardiac hypertrophy. However, from Tigerstedt's initial discovery, there was a long and arduous transformation of ideas and paradigms that eventually translated to clinical applications. Although the role of the renin-angiotensin system in the pathophysiology of hypertension and heart failure was suspected through the years, beneficial effects from its blockade were not realized until the early 1970s. Thus, this story starts with a short historical perspective that provides the reader some insight and appreciation into the long delay in translation.

The synthesis of a tetradecapeptide renin substrate

A tetradecapeptide renin substrate having a biological activity comparable to the natural product and similar chemical properties has been synthesized by means of the carbobenzyloxyl azide and mixed anhydride methods.

Renin-angiotensin system stimulates cardiac and renal disorders in Tsukuba hypertensive mice

1. The role of the renin-angiotensin system (RAS) in cardiac hypertrophy and nephropathy was examined in Tsukuba hypertensive mice (THM) carrying both human renin and angiotensinogen genes. 2. Tsukuba hypertensive mice were treated with 20 mg/kg per day lisinopril, 30 mg/kg per day hydralazine or nothing. Administration of drugs was performed for 6 months from 12 weeks of age; water intake and urine volume were measured and urine albumin excretion, heart to bodyweight ratio and the glomerulosclerosis index were examined. 3. Systolic blood pressure was significantly lowered by treatment with lisinopril and hydralazine. Urine volume, water intake and urinary albumin excretion were significantly decreased by lisinopril. When hydralazine was administered to THM, these parameters were transiently decreased, but eventually reached almost the same levels as those in the untreated group. The heart to bodyweight ratio was significantly decreased by lisinopril, but not by hydralazine. The glomerulosclerosis index was significantly lowered by lisinopril, but the index in the hydralazine group was not significantly different from that in the untreated group. 4. These results suggest that the RAS plays an important role in the progression of cardiac hypertrophy in THM. In addition, the RAS may also play an important role in the progression of nephropathy; however, this may also be partially regulated by elevated blood pressure in the short term.

General and pulmonary hemodynamic effects of pure decapeptide angiotensin in normotensive man

Purified natural decapeptide angiotensin was infused intravenously at a constant rate for 32 minutes in 5 normotensive subjects. There was no significant change in the cardiac output. There were significant increases in the pulmonary artery, the pulmonary wedge, and the brachial artery pressures. There were significant increases in the systemic vascular and the total pulmonary resistances. There was no significant change in the pulmonary arteriolar resistance. The data indicate that angiotensin I produces peripheral arteriolar constriction and fail to demonstrate a concomitant pulmonary arteriolar constriction. Thus, they are consistent with an hypothesis implicating angiotensin as a causative agent in human essential hypertension.

The purification and partial characterization of several forms of hog renin substrate

Hog renin substrate has been separated into three major (A, B, and C) and two minor forms (D and E) by DEAE cellulose chromatography. Two of the major forms (B and C) have been further fractionated into two additional types (1 and 2) by countercurrent distribution. The purification of substrates A, C₁, and C₂ has been completed. Analysis shows that all three are glycoproteins with molecular weights of about 57,000, and have similar amino acid compositions. Differences exist in the sialic acid, glucosamine, and neutral hexose content, which may account for different physical properties. All the forms of the substrates are attacked by renin at similar rates, and appear to yield the same angiotensin I.

THE PRESENCE OF RENIN ACTIVITY IN BLOOD VESSEL WALLS

The preparation, of an extract of hog blood vessels and organs containing renin activity has been described. The extract hydrolyzes natural or synthetic renin substrate to form a vasopressor material. This reaction could not be distinguished from the hydrolysis of renin substrates by kidney renin. The activation energy, effect of substrate concentration on velocity, inhibition by antirenin, and pH optimum of the extract and of kidney renin are the same. Renin activity is found in the adventitia and media of the aorta, the liver and, to a lesser extent, in other vascular organs.

PLASMA VASOCONSTRICTOR ACTIVITY IN PATIENTS WITH RENAL, MALIGNANT, AND PRIMARY HYPERTENSION

Polypeptide vasoconstrictor activity was assayed in the peripheral venous blood of 45 hypertensive patients and 20 normal subjects. The average activity was significantly increased in all hypertensive groups, and activity tended to be much higher in patients with renovascular and malignant hypertension than in primary hypertension.

In confirmation of previously reported results by Helmer and Judson, there was no correlation between vasoconstrictor activity and renal excretory function. The plasma level of vasoconstrictor activity did not correlate with mean arterial pressure except when malignant or renovascular hypertension was present.

A significant inverse relationship was found between the serum potassium concentration and vasoconstrictor activity: as activity levels increased, the potassium fell. The data suggest that a renin-like substance may be present in various hypertensive states in amounts sufficient to depress serum potassium, presumably by activation of the renin-angiotensin-aldosterone mechanism.

PLASMA RENIN ACTIVITY IN ACUTE TUBULAR NECROSIS AND OTHER RENAL DISEASES ASSOCIATED WITH HYPERTENSION

By in vitro and in vivo bioassay methods, activity of plasma renin was studied in patients with acute tubular necrosis, polyarteritis, systemic lupus erythematosus, or the terminal stage of chronic renal disease.

Plasma renin activity was increased during the oliguric phase of acute tubular necrosis, polyarteritis, or systemic lupus erythematosus; it was not increased during the diuretic phase of acute tubular necrosis and in the terminal stage of chronic renal disease.

Acute reversible hypertension, observed in some patients during the oliguric phase of acute tubular necrosis, vas associated with a marked increase in plasma renin. A similar association was observed in hypertensive patients with polyarteritis or systemic lupus erythematosus, but not in hypertensive patients with the terminal stage of chronic renal disease. These data suggest that the renin mechanism may participate in the acute hypertension of acute tubular necrosis, polyarteritis, and systemic lupus erythematosus, but not in chronic hypertension in the present study.

Renal parenchymal involvement in essential hypertension

This article has reviewed the involvement of the kidney as a target organ of essential hypertension. Since Bright first made the association of renal disease and hypertension in 1836, the nature of this relationship has been debated. Although there is evidence implicating abnormalities of renal function in the pathogenesis of essential hypertension, hypertension frequently precedes histologic evidence of alterations in renal structure. Nephrosclerosis, or hardening of the kidney, is the term used to describe the histologic changes occurring in the kidney as the result of hypertension. It can be though of as an acceleration of the normal aging process of the renal vasculature. Glomerular and tubular changes have been traditionally thought to be ischemic in origin. Experimental evidence supports the notion that, as renal function is lost, intraglomerular hypertension develops and may be responsible for additional nephron loss in hypertension. This idea may have therapeutic implications for hypertensive patients with renal insufficiency in that agents that reduce both systemic and intraglomerular pressure may be preferable. Hemodynamically, early hypertension is often characterized by normal peripheral and renal vascular resistance and an increased cardiac output. In established hypertension, cardiac output is usually normal, and peripheral and renal vascular resistances are increased. Renal blood flow is reduced, glomerular filtration rate is maintained, and the filtration fraction rises. In the absence of an accelerated malignant phase, renal failure is uncommon in essential hypertension. Males and blacks are most sensitive to the vascular damage of essential hypertension. Essential hypertension remains an important cause of end-stage renal disease, especially in blacks. Atherosclerotic obstruction of the renal arteries may be a more common cause of renal failure in patients with essential hypertension than has been previously recognized. There are few sensitive markers of early renal involvement in essential hypertension. Several studies of sensitive markers are promising and may detect patients who are prone to renal injury and deserve more aggressive treatment. Malignant hypertension is characterized pathologically by vascular changes of proliferative endarteritis and fibrinoid necrosis. Fortunately, its frequency is decreasing because of early identification and effective treatment of essential hypertension. Effective treatment of severe and malignant hypertension clearly leads to stabilization (and occasionally improvement) of renal function.(ABSTRACT TRUNCATED AT 400 WORDS)

Malignant or accelerated hypertension

Malignant or accelarated hypertension is a life-threatening medical emergency that is a possible complication of practically any hypertensive disorder. If not promptly treated it can cause severe, rapidly progressive target-organ damage and death. While the histo-pathologic features of malignant hypertension are well recognized, the pathogenesis of the associated vascular lesions and the transition from a benign to a malignant phase are unclear. With adequate control of hypertension, progression to the accelarated or malignant phase can be prevented. Moreover, promptly and effectively reducing the blood pressure during the malignant phase can prevent, minimize or even reverse serious target organ injury. Malignant hypertension, therefore, is both preventable and treatable.

A highly sensitive cytochemical bioassay for plasma angiotensin II

A highly sensitive cytochemical bioassay has been developed for measuring angiotensin II in human plasma. The assay depends on the ability of angiotensin II to alter the reducing potency of the zona glomerulosa as measured by Prussian blue staining and microdensitometry. An inverse correlation between the intensity of the stain and the logarithm of concentration existed over the range 0.05-5.0 fmol/1 of angiotensin II. The limit of sensitivity of the assay in plasma was 50 fmol/1; the index of precision was 0.07 +/- 0.04 (mean +/- SD; n = 15); and the coefficient of variation of a quality control sample was 34%. The response was specific for angiotensin II; approximately 10(2) times more angiotensin III and approximately 10(6) times more ACTH was required to produce a similar effect. Angiotensin I had no significant activity. A significant inverse relationship existed between sodium intake and bioactive angiotensin II in 5 normal subjects studied on low, normal and high sodium diets. Extremely low levels of angiotensin II were detected in anephric subjects.

High sodium-low potassium environment and hypertension

The high sodium-low potassium environment of civilized people, operating on a genetic substrate of susceptibility, is the cardinal factor in the genesis and perpetuation of "essential" hypertension. The noxious effects begin in childhood, when habits of excess salt consumption are acquired at the family table, and are perpetuated by continuing habit and by increasing use of convenience and snack foods with artificially high concentrations of sodium and low levels of potassium. Present methods of food preparation leach out the protective potassium. Extradietary sodium chloride is a condiment not a requirement. Some primitive populations clearly preferred potassium chloride to sodium chloride. Chronic expansion of extracellular fluid volume induced by excess salt consumption causes the central and peripheral circulatory regulatory mechanisms to work at cross purposes, resulting in increased arterial pressure. The protective effect of potassium is dramatic and easily demonstrable in animals and man but its mechanism is not known. It cannot be entirely a direct effect on blood pressure because rats protected with extra potassium against a moderately high salt intake live much longer than control rats but have the same elevated blood pressures. In hypertension with a demonstrable "cause," the high sodium-low potassium environment makes a bad matter worse. In nature, feral man and his forebears were not confronted with excessive sodium and deficient potassium; indeed, the reverse was the case. Evolution has provided powerful mechanisms for conserving sodium and eliminating potassium, but no efficient physiologic mechanisms for conserving potassium and eliminating excess sodium. Most laboratory animal "control" diets contain an amount of sodium that fully suppresses aldosterone secretion, and the same is true of the "average" diet of the American people. Inadequate attention to dietary sodium and potassium makes many studies in both animals and man of uncertain validity. Internally, essential hypertension is an exceedingly complex mosaic of physiologic interactions. Viewed from outside, it is a disorder for which genetic material sets the stage; excessive sodium precipitates it and perpetuates it. Extra salt makes all forms more rapidly progressive and accelerates the onset of terminal events; extra potassium is everywhere protective. When an entire population eats excessively of salt, hypertension will develop among those genetically susceptible, but epidemiologic studies of salt versus blood pressure will not show a relation of salt to hypertension. This is the saturation effect. Low sodium diets are therapeutically effective but generally regarded as an impossible or an unnecessary nuisance. Effective prevention programs must be instituted at as early an age as possible. The efficacy of a prophylactic/therapeutic low sodium-high potassium diet should be weighed against the uncertain hazards of a lifetime of pill taking.

The biochemistry of the renin-angiotensin system and its role in hypertension

The renin-angiotensin system has an important role in maintaining elevated blood pressure levels in certain forms of experimental and human hypertension. Renin, an enzyme produced by the juxtaglomerular cells of the kidney, acts on a protein substrate found in the alpha 2-globulin fraction of the plasma to produce a decapeptide, angiotensin I. This decapeptide is not directly pressor, but on passage through the pulmonary circulation is converted to an octapeptide, angiotensin II, a very potent pressor substance which acts by causing constriction of arteriolar smooth muscle. In addition to its direct action which increases blood pressure, angiotensin II acts on the adrenal cortex to cause the release of the sodium-retaining hormone aldosterone. Recent evidence suggests that this action may be mediated by the heptapeptide, angiotensin III. Both renin and its protein substrate exist in multiple forms and renin may also exist as a high molecular-weight "pro-hormone," although the physiologic significance of these forms is not clear. The elucidation of the biochemistry of the renin-angiotensin system has provided us with inhibitors which allow the system to be blocked effectively in vivo. Thus, angiotensin antagonists such as Sar 1, IIe 8-angiotensin II and converting enzyme inhibitors such as BPP 9a (SQ 20881) have proved useful in the study of experimental and human hypertension.

The Metabolism of Angiotensin II

1. I 131 -labeled angiotensin II has been employed to study the metabolism of this polypeptide.

2. Following the intravenous administration of angiotensin II-I 131 to normotensive and untreated primary benign hypertensive subjects, a slower angiotensin II degradation rate and a larger final volume of distribution of angiotensin II-I 131 was found in the hypertensive than in the normotensive patients. The slow rate of degradation of angiotensin II may be responsible for the increased quantity and concentration of this polypeptide in the body fluids.

3. Greater quantities of angiotensin II-I 131 are degraded in vitro by sera from untreated primary benign hypertensive patients than from normotensive or secondary renal hypertensive patients. There is evidence for the presence of a serum factor or factors enhancing angiotensin II-I 131 degradation and for the presence of a heat labile inhibitor.