Plasma Angiotensinase Activity in Patients With Hypertension and Edema*

Abstract

An abnormal metabolism of angiotensin II in essential hypertension has been suggested by several studies. Wood (1) reported that the venous blood of hypertensive patients showed a decreased capacity to inactivate an in vitro admixture with synthetic angiotensin' as judged by the pressor response on reinfusion into the hypertensive donors. Wolf and associates reported a prolonged radiochemical half-life of I131-labeled angiotensin in hypertensive patients after intravenous administration (2), but found a shortened radiochemical half-life in a purely in vitro system (3). Klaus (4) described a system in which the measurement of the amount of valine freed from synthetic valyl-5-angiotensin II after an in vitro admixture with plasma was equated to angiotensinase activity and reported no significant difference between hypertensive and normotensive plasma.Thus in vitro chemical methods leave the difficult problem of equating the chemical end-point to residual biological activity. It seemed that an in vitro system employing the loss of pressure response in a standard bioassay rat preparation to the serial injection of an admixture of plasma and angiotensin might obviate some of these difficulties and contribute to an understanding of this intricate problem. MATERIALS AND METHODSA. The assay. An in vitro admixture of synthetic angiotensin II 1 and plasma was studied for the progressive loss of pressor activity by serial inj ections into a 250-g vagotomized rat prepared with 'Nembutal and pentolinium. The left jugular vein was cannulated with polyethylene tubing and injected with a microsyringe containing a standard (1 /Ag per ml) dilution of angiotensin II (preserved as a 20%o ethanol solution). The right jugular vein was similarly connected to a microsyringe containing a mixture of 1 ml of the standard angiotensin solution and 1 ml of plasma. A stop watch was started at the time of the admixture, and room temperature was constant at 25 + 10 C. Alternate equal doses of standard angiotensin solution and standard solution mixed with plasma were administered every 3 to 4 minutes. The right carotid artery was cannulated with polyethylene tubing and the arterial pressure response recorded on a direct-writing pen-float mercury manometer. At the top of Figure 1 is shown the rat's pressure recording in a study on the plasma from a normotensive subject. The hatched spikes represent the serial pressure response of the plasma-angiotensin mixture and show the progressive reduction in the response; the nonhatched spikes represent the serial pressure response of the standard angiotensin solution alone and show full sensitivity of the rat to the serial injection of 10 m/Ag throughout the study. Variations, particularly a decrease of the standard response by more than 2 mm, are unsatisfactory and indicate that the study should be repeated. A minimal rat sensitivity of 1 mm Hg pressure rise per m/Ag of injected angiotensin is required. In a given study the serial dose was either 5, 10, or 15 m/Ag, whichever was necessary to ensure a pres...

Plasma Vasoconstrictor Activity in Patients with Renal, Malignant, and Primary Hypertension

“…If the activity measured is actually renin-induced, assay results might be modified by the availability of renin substrate in the plasma.23 On the other hand, plasma angiotensinase is essentially inactive at the pH used in this assay. Elevations in plasma angiotensinase activity described in some hypertensive states 28 would not influence the results significantly.…”

Role of Histamine in Producing the Eosinophilia of Magnesium Deficiency.

“…The acute phase of the magnesium deficient syndrome is characterized by a dermal hyperemia (6) in rats and dermal mast cells degranulate in this phase (3). Administration of heparin in combination with histamine also failed to significantly elevate the number of circulating eosinophils (Table I, Groups 4,5). However, administration of commercial histamine, (Table I, Groups 1, 2, 3) in a variety of doses, routes and time intervals (some not reported here) failed to duplicate the eosinophilia produced by magnesium deficiency.…”

Leucine aminopeptidase M-induced reductions in blood pressure in spontaneously hypertensive rats.

“…Thus, although SHR showed the greatest drop in heart rate across pretreatments, the pattern of LAP-M-induced changes in heart rate were very similar in members of the two strains over the conditions we used. Discussion The suggestion that angiotensinases play a role in the pathogenesis of hypertension was originally offered by Hickler et al 13 and Itskovitz et al However, data to support this hypothesis as it pertains to a central mechanism are only now becoming available. Along these lines our laboratory has been investigating procedures to manipulate the half-lives of brain-synthesized Ang II and Ang III initially by employing aminopeptidase inhibitors.…”