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Biomedical subjects

F H Derkx

Publications and source records attributed to F H Derkx.

153 records · Page 9Linked to original sources
PubMed1978

Renal release of active and inactive renin in essential and renovascular hypertension.

1. Active and acid-activable inactive renin were measured in renal venous and arterial plasma of 18 patients with essential hypertension (EHT) and 19 patients with renovascular hypertension (RVHT). In seven patients with EHT and in 11 patients with RVHT measurements were made before and 25-35 min after an intravenous injection of 300 mg of diazoxide. 2. Under basal conditions the renal vein to artery ratios for active and inactive renin in EHT ranged from 0.71 to 1.96 and from 0.68 to 1.44 respectively. In 14 patients with RVHT the renal vein to artery ratio for active renin on the affected side was above the range found in EHT and in six of them the renal vein to artery ratio for inactive renin was also elevated. 3. The diazoxide-induced release of active renin from kidneys, which had a stenotic artery but were not seriously contracted, was associated with a fall of the renal vein to artery ratio for inactive renin to a value below 1.00. 4. The results indicate that changes in the release of active and inactive renin do not always run in parallel. The findings are compatible with the hypothesis that circulating inactive renin can be activated in the kidney.

Diazoxide↗
PubMed1978

Renal secretion of inactive renin.

Human plasma contains a non-dialyzable factor which is not enzymatically active in its native form but shows renin-like activity after exposure to low pH (inactive renin). In 3 out of 13 patients with renovascular hypertension the renal to peripheral vein ratio for inactive renin on the affected side was above 1.40, indicating renal release of this form of renin. In 4 cases a high renal to peripheral vein ratio for active renin was associated with a ratio for inactive renin below 0.80, indicating renal activation of circulating inactive renin. The results suggest a renal mechanism for modulating the degree of activation of renin. They have some practical implications for the pre-operative evaluation of patients with renovascular hypertension.

Humans↗
PubMed1977

Volume-pressure relationships during development of mineralocorticoid hypertension in man.

Serial measurements of urinary sodium excretion, sodium space, plasma volume, and plasma renin concentration were made during the development of hypertension in patients who were exposed to an excess of endogenous or exogenous mineralocorticoid activity. Five patients with primary aldosteronism due to adenoma were followed during spironolactone treatment, for 35-55 days after the drug had been stopped, and finally, after surgery. Blood pressure rose continuously after stopping spironolactone. Sodium balance, however, showed an initial phase of sodium gain, followed by a phase of gradual sodium loss. Sodium space and exchangeable sodium rose by 5.0 +/- 0.48 liters/1.73 m2 of body surface area (BSA) (P less than 0.005) and by 865 +/- 97 mEq/1.73 m2 BSA (P less than 0.005), respectively; the values were maximal after 10-15 days, declined afterward, but remained higher than during spironolactone treatment. Plasma and blood volumes rose by 624 +/- 90 ml/1.73 m2 BSA (P less than 0.005) and by 327 +/- 74 ml/1.73 m2 BSA (P less than 0.01), respectively; they were maximal after 20-25 days, and then returned to their initial values. Exchangeable sodium, during the phase of sodium loss, was inversely correlated with the rise in blood pressure (P less than 0.01). Renin fell during the phase of sodium gain, and remained low afterwards. Blood pressure and sodium space declined after surgery, but plasma volume showed no change. The postsurgery values of these parameters were not significantly different from those measured during spironolactone treatment. Two subjects with adrenocortical insufficiency, who were followed for 45-60 days during treatment with dexamethasone and 9alpha-fluorocortisol acetate, also showed a transient rise in sodium space and plasma volume. The results suggest a redistribution of body fluids during development of hypertension. They also suggest that the tendency of body fluid volumes to return to normal is pressure-dependent. The long-term effects of mineralocorticoid excess on the interrelations between pressure, volume, and renin bear some resemblance to the pattern observed in patients with established essential hypertension, i.e., pressure remains elevated despite a decrease of volume, and renin is "inappropriately" suppressed in relation to the sodium and volume status.

Adenoma↗
PubMed1976

Inactive renin in human plasma.

Human plasma contains renin, which is enzymatically active at neutral pH (active renin), and a non-dialysable factor, which has renin-like activity after treatment at low pH (inactive renin). In vitro activated plasma-renin and purified human renal renin showed identical enzyme-kinetic properties. Quantitative estimations of inactive renin in renal venous plasma from 5 patients with renal-artery stenosis demonstrated its release by the kidney. Acute stimulation of renin release by isoprenaline, tilting, or diazoxide in 13 normotensive individuals and in 9 patients with essential hypertension increased active plasma-renin and reduced inactive plasma-renin. Inactive plasma-renin was increased and active plasma-renin decreased during suppression of renin release by propranolol in 12 patients with essential hypertension. In 55 patients with various disorders, inactive and active plasma-renin were directly correlated. However, the concentration of inactive renin, for a given value of active renin, varied widely from patient to patient. These results indicate that so-called inactive renin is indeed physiologically related to active renin. They also suggest that inactive renin can be activated not only in vitro, but also in vivo. Different renin assays measure different relative amounts of active and inactive renin. This may call for reinterpretation of results obtained by various methods, especially in situations where changes in plasma concentrations of the two forms of renin are in opposite directions.

Adult↗
PubMedDate not supplied

Asynchronous changes in prorenin and renin secretion after captopril in patients with renal artery stenosis.

An assay of plasma prorenin was developed in which the conversion to renin occurred under apparently optimal conditions. Some characteristics of the assay were 1) prorenin was activated by Sepharose-bound trypsin at 4 degrees C; 2) the concentration of activator was not critical provided that incubation was prolonged until renin activity had reached a plateau; and 3) this plateau was stable and had the same height as after maximal activation with acid, pepsin, plasmin or urokinase. Maximal activity with Sepharose-bound trypsin at 4 degrees C was higher than with cryoactivation, and optimal conditions were more readily reproduced than with trypsin at 37 degrees C or with acid-activation. The assay was used for measurements in peripheral and renal vein plasma after captopril in hypertensive patients with unilateral renal artery stenosis. Peripheral renin rose within 30 minutes after a first dose of captopril, 50 mg orally, and it remained high with chronic treatment. In contrast, peripheral prorenin fell initially and rose after 4 hours. These changes in peripheral plasma were related to changes in the secretion rates of the two forms of renin from the affected kidney. Thus chronic, but not acute, stimulation of renin release was associated with an increased secretion rate of prorenin. The late rise in prorenin is probably an indication of enhanced synthesis in the kidney, so that more prorenin is available for conversion. The data suggest that prorenin is indeed a biosynthetic precursor of renin and that, at least under certain circumstances, a major proportion of circulating prorenin originates from the kidney.

Captopril↗
PubMedDate not supplied

Effects of selective and nonselective beta-agonists on plasma potassium and norepinephrine.

The effects of graded infusions of the beta-agonists isoproterenol (nonselective), l-prenalterol (beta 1-selective), and salbutamol (beta 2-selective) on plasma potassium and norepinephrine were compared in subjects with borderline hypertension. Potassium levels fell with all three agonists, and norepinephrine levels rose with isoproterenol and salbutamol. These effects on potassium and norepinephrine were closely correlated and occurred at the same dose ranges as the cardiovascular responses. The fall in plasma potassium was probably caused by activation of beta-receptors, mainly on skeletal muscle, with subsequent stimulation of active sodium-potassium transport across the cellular membrane. The rise in plasma norepinephrine may have been due to activation of beta-receptors on sympathetic nerve endings. Activation of these presynaptic receptors is known to enhance the release of norepinephrine during nerve stimulation. For a given increase in heart rate and cardiac contractility, as measured by the heart rate-corrected duration of total electromechanical systole, which are mainly beta 1-responses, the effects on potassium and norepinephrine were in the order: salbutamol greater than isoproterenol greater than prenalterol. beta-Blockade with propranolol (nonselective), 80 mg four times a day, or atenolol (beta 1-selective), 100 mg once a day, antagonized the hypokalemic effect of isoproterenol as well as the rise in norepinephrine, but when isoproterenol was infused in doses high enough to overcome the blockade of the heart rate response, the effects on norepinephrine and potassium were abolished by propranolol and not by atenolol. Thus, the receptors in question appear to be of the beta 2-subtype.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Agonists↗