Age versus urinary sodium for judging renin, aldosterone, and catecholamine levels: studies in normal subjects and patients with essential hypertension

Comparative evaluation of the new vasodilator carprazidil and minoxidil in the treatment of moderate to severe hypertension

The efficacy and side effects of the new vasodilator carprazidil and the established vasodilator minoxidil were compared in 18 hypertensive patients inadequately controlled by 2 to 4 conventional drugs; the latter included diuretics, beta-blockers and/or sympatholytics and, in half the cases, vasodilators, such as hydralazine, diazoxide or the postsynaptic alpha-blocker prazosin. The vasodilators were withdrawn and, using a crossover design all patients received carprazidil (mean final dose 88 mg) and minoxidil (20 mg) for an average period of 5 to 6 months. The effects of the 2 agents appeared to be qualitatively and quantitatively similar. Both tended to cause sodium retention and an increase in heart rate, which required an increased dose of diuretic in one third of the cases or of a beta-blocker in a quarter. With this approach mean body weight and blood volume were not altered in the established phase of carprazidil or minoxidil treatment; heart rate and plasma norepinephrine tended to be only minimally increased, plasma renin was slightly increased, and plasma aldosterone and epinephrine were largely unchanged. Supine and upright blood pressure were reduced from initial values of 189/113 and 167/ 113 mm Hg, to 149/95 and 138/95 mm Hg (-18 and - 17%), respectively, during carprazidil, and to 154/95 and 141/96 mm Hg (-17 and - 15%) during minoxidil therapy. Hypertrichosis occurred with both agents in almost all patients, and limits their more prolonged use in females. No adverse side effects on haematological parameters, liver or renal function were observed, nor was antinuclear antibody detected. It is concluded that carprazidil and minoxidil are equivalent vasodilator agents in the treatment of severe hypertension, particularly in males.

Catecholamines, renin, aldosterone, and blood volume during chronic minoxidil therapy

Several pressor factors were studied before and during chronic minoxidil therapy (median dose 27.5 mg/day) in 16 patients with hypertension that was refractory to conventional drugs. Following treatment with minoxidil and intensified diuretic therapy, blood pressure was decreased markedly; pulse rate, body weight, plasma volume, plasma aldosterone and epinephrine levels were not significantly altered, while plasma renin activity tended to be increased. Supine and upright plasma norepinephrine concentrations were increased by 140 (P less than 0.005) and 50% (P less than 0.05), respectively, but no significant change in urinary norepinephrine excretion was apparent. The latter parameter may not be a close index of sympathetic activity in patients with severe hypertension treated with minoxidil. While a search for underlying pheochromocytoma is always indicated in refractory hypertension, it appears mandatory to evaluate plasma catecholamines prior to or following discontinuation of treatment with minoxidil, to avoid a wrong diagnosis of pheochromocytoma.

Exaggerated pressor responsiveness to norepinephrine in nonazotemic diabetes mellitus

Pressor responses to norepinephrine (NE) or angiotensin II (AII) were studied in 27 diabetic patients without heart or renal failure and in 27 normal subjects. Mean plasma or 24-hour urinary sodium, blood volume and preinfusion plasma NE levels were similar in diabetic and normal subjects; exchangeable sodium was higher (p less than 0.02) and preinfusion plasma renin activity (PRA) was slightly lower in diabetic patients. The NE pressor and threshold doses were lower in diabetic patients than in normal subjects (76 versus 141 and 16 versus 41 ng/kg/min, respectively; p less than 0.05). The AII pressor dose also tended to be lower in diabetic patients (7.2 versus 11.9 ng/kg/min; p less than 0.05), but the AII threshold dose did not differ between the two groups (1.1 versus 1.6 ng/kg/min). These findings were similar in the diabetic subgroup without or with retinopathy (N = 13 and 14, respectively) and in those with normal or high blood pressure (N = 17 and 10, respectively). These observations suggest that in nonazotemic diabetes mellitus increases in AII pressor responsiveness are associated with a concomitant reduction in PRA. However, cardiovascular pressor responsiveness to NE tends to be exaggerated despite normal plasma NE levels and this alteration may occur already in the normotensive stage of diabetes mellitus. Cardiovascular hyperresponsiveness in diabetic subjects may be related to excess body sodium or structural alterations in the vasculature, or both.

Correction of altered noradrenaline reactivity in essential hypertension by indapamide

Fourteen patients with untreated mild to moderate essential hypertension had on average an abnormally high cardiovascular reactivity to exogenous noradrenaline and angiotension II, while plasma noradrenaline, renin activity, exchangeable body sodium, and blood volume were normal. Treatment with a low dose of indapamide (2.5 mg/day) for six weeks decreased blood pressure by 10% in these hypertensive patients but not in 13 normal control subjects. Plasma or blood volume and exchangeable sodium were not changed significantly; nevertheless, the latter, and body weight, tended to be decreased slightly. Though a mild reduction in extracellular sodium in both normal and hypertensive subjects appears possible, it may not per se fully explain indapamide's blood pressure-lowering effect in essential hypertension. Indapamide induced a mild decrease in angiotensin II pressor responsiveness in normal or hypertensive subjects, but a possible depressor influence from this change was probably antagonised by a concomitant pronounced increase in plasma renin activity. In hypertensive patients, the abnormally high noradrenaline reactivity was corrected by indapamide without an accompanying increase in endogenous plasma noradrenaline levels. Indapamide-induced changes in blood pressure correlated with those in noradrenaline pressor dose. It was concluded, therefore, that indapamide may decrease blood pressure in essential hypertension at least in part by lowering an abnormally high cardiovascular noradrenaline reactivity without causing an equivalent increase in adrenergic nervous activity.

Plasma norepinephrine during stress in essential hypertension

Comparative studies of plasma norepinephrine in patients with essential hypertension and in normotensive controls have consistently reported higher mean resting levels of norepinephrine in the hypertensive groups, but the hypertensive-normotensive differences have often been small and, in about three-fifths of the studies, not statistically significant. The author reviewed the medical literature to test the hypothesis that, during stress, hypertensive-normotensive differences in norepinephrine become more apparent. Among 24 studies involving orthostatic stress, the increment in norepinephrine with standing was similar for hypertensives and normotensives (239 vs 230 pg/ml). In contrast, among eight studies involving exercise, the increment in norepinephrine was significantly greater in hypertensives (834 vs 450 pg/ml). For both standing and isotonic exercise, absolute changes in norepinephrine with stress correlated with basal norepinephrine across the hypertensive but not the normotensive groups. These results are consistent with the existence within the hypertensive population of a subgroup of patients with elevated norepinephrine levels at rest and excessive sympathetic responsiveness to stress. However, the available literature is decidedly lacking in studies about other types of stress besides standing and exercise.

Relationship between plasma catecholamines and urinary catecholamine excretion rates in normal subjects and certain diseased states

Relationships between plasma norepinephrine (PNE) or epinephrine (PE) and urinary norepinephrine (UNE) or epinephrine (UE) excretion rates were studied in 37 normal subjects, 39 patients with benign essential hypertension, 23 with unilateral renal hypertension, and 20 with bilateral renal disease (serum creatinine 2.3 +/- 2.6 mg/100 ml). measurements were also performed after 6 weeks of diuretic treatment in 27 normal subjects and all patients with essential hypertension. In the untreated state, PNE and UNE values were generally normal in essential or unilateral renal hypertension; PNE tended to be decreased in diabetics and increased in bilateral renal disease. Diuretic treatment caused a tendency for slightly increased PNE and UNE. UNE correlated significantly with supine PNE or upright PNE or their mean value, and this relationship appeared to be comparable between untreated normal subjects and the various patients groups, except for a tendency for slightly higher PNE at given UNE values in bilateral renal disease. No significant correlations between UE and PE were apparent in the normal subjects or patient groups. These data demonstrate a dissociation of UE from PE levels. In contrast, UNE is an approximative index of PNE, and this relationship appeared to be generally unaltered in essential or unilateral renal hypertension. In patients with bilateral renal disease the slight shift of this relationship indicates that consideration of renal function is necessary for interpretation of NE levels.

Effect of age on active and inactive plasma renin in normal subjects and in patients with essential hypertension

The effect of age on the levels of active and trypsin-activatable inactive plasma renin was examined in 41 normal subjects and 54 patients with essential hypertension, during recumbency and after stimulation with furosemide and ambulation. Active renin levels in supine subjects and patients decreased with age. Inactive renin levels did not change with age in normal subjects, whereas in hypertensive patients they decreased with age. Following stimulation with furosemide and ambulation, the levels of active renin increased but the responsiveness to stimulus decreased with age in both groups. In contrast, inactive renin levels slightly increased after furosemide administration and ambulation, resulting in increased proportion of active to total renin. These data show that an acute stimulation with furosemide and ambulation affects mainly the active form of plasma renin, and the effect of age on inactive plasma renin in normal subjects may be different from that in patients with essential hypertension.

Acute hypercalcemic hypertension in man: role of hemodynamics, catecholamines, and renin

The effect of acute hypercalcemia on blood pressure, blood volume, hemodynamic parameters, plasma norepinephrine, epinephrine, dopamine, renin, and aldosterone concentrations was investigated. After 1 hour of equilibration, 10 patients received an infusion of calcium gluconate in 5% dextrose (calcium 15 mg/kg of body wt in 3 hours). The calcium infusion increased the mean serum calcium from 8.7 to 13.0 mg/dl, the systolic blood pressure from 144 +/- 10 to 184 +/- (SEM) 12 mm Hg (P less than 0.001), the diastolic pressure from 78 +/- 4 to 93 +/- 5 mm Hg (P less than 0.01). The plasma volume was decreased by 9% (P less than 0.001), whereas the hematocrit was increased (P less than 0.05). Heart rate and cardiac output remained unchanged. Total peripheral resistance was increased from 1643 +/- 223 to 2256 +/- 387 dyne.sec/cm5 (P less than 0.05). The plasma epinephrine concentration rose from 4.5 +/- 0.7 to 6.9 +/- 1.2 ng/dl (P less than 0.01). The plasma norepinephrine concentration was unchanged after 2 hours and increased only slightly after 3 hours of calcium infusion. Plasma renin, aldosterone, and dopamine concentrations were not significantly changed. These findings demonstrate that acute hypercalcemic hypertension is mediated by an increase in peripheral vascular resistance. Hypercalcemic hypertension may be induced by a direct effect of calcium on blood vessels; calcium-mediated increase in adrenal epinephrine release may play a mild contributory role, and plasma volume contraction, an inhibitory role.

Plasma aldosterone response to angiotensin II in sodium-restricted elderly subjects with essential hypertension

The plasma aldosterone (PA) response to sodium restriction (25 mEq daily for 4 days) and to graded infusions of angiotensin II (AII, 2, 4 and 8 ng/kg/min each for 30 min) during a low-sodium intake were studied in 15 elderly subjects with mild essential hypertension versus 10 elderly normotensive subjects. The PA response to sodium restriction relative to changes in plasma renin activity (PRA) was estimated by the ratio of PA increment to PRA increment after sodium restriction (delta PA/delta PRA). THe PA response to graded AII infusions was determined by the increment of PA above the basal level after each dose of AII. In 10 of the 15 elderly hypertensive subjects whose PRAs responded normally to sodium restriction, the delta PA/delta PRA ratios and PA increments during the graded AII infusions were similar to those in the elderly normotensive subjects. However, in the remaining 5 elderly hypertensive subjects whose PRAs responded subnormally to sodium restriction, the delta PA/delta PRA ratios were high and the PA increments greater during the graded AII infusions. THe increments of mean blood pressure during the graded AII infusions were similar in the foregoing 10 of 15 hypertensive subjects, and significantly greater during the AII infusion rates of 4 and 8 ng/kg/min in the remaining 5 hypertensive subjects when compared with those in the normotensive subjects. Apparently some subjects with essential hypertension, whose PRAs response subnormally to sodium restriction, have an abnormally enhanced adrenal responsiveness to AII under the conditions of low-sodium intake.

Sodium, potassium and age: possible determinants of plasma renin activity and aldosterone during childhood (age 4-16)

The renin-angiotensin-aldosterone system was studied in fifty healthy children aged 4-16 years under normal sodium and potassium intake. The plasma renin activity (PRA) and plasma aldosterone (PA) decreased with age: r = -0.30, P less than 0.05 for plasma renin activity and r = -0.33, P less than 0.05 for plasma aldosterone. Significant negative correlation was obtained between plasma renin activity and the 24-h urinary sodium excretion; r = -0.40, P less than 0.01. This relationship remained significant when the daily urinary sodium excretion was corrected for 1.73 m2 body surface area (BSA); r = -0.40, P less than 0.01. Using the multivariance analysis, plotting the plasma renin activity against the two combined parameters (24-h urinary sodium excretion and age), no improvement was obtained (r = 0.38, P greater than 0.05). This finding suggests that during childhood, sodium rather than age has a major modulatory role on plasma renin activity. With advancing age the plasma aldosterone showed a significant positive correlation coefficient with plasma renin activity(r = 0.29, P less than 0.05). Multivariance analysis between plasma aldosterone and the two combined parameters, Plasma renin activity and age, significantly improved the correlation coefficient (r = 0.42, P less than 0.05) suggesting that both plasma renin activity and age play a dominant modulatory role in the control of plasma aldosterone during childhood. Neither 24-h urinary sodium excretion, nor 24-h urinary potassium excretion, improved the multiple correlation coefficient with plasma aldosterone when added to plasma renin activity and age.

Pressor factors and cardiovascular pressor responsiveness in borderline hypertension

The role of various pressor factors and cardiovascular responsiveness to norepinephrine or angiotensin II in the pathogenesis of borderline hypertension was evaluated. Exchangeable body sodium, blood volume, plasma renin activity, norepinephrine or dopamine levels, and norepinephrine or epinephrine excretion rates were similar between 24 patients with borderline hypertension (mean age 34 +/- 4 (SEM) years and 22 normal subjects matched for age; the patients had a slight increase in supine plasma epinephrine. Pressor doses of norepinephrine or angiotensin II were significantly lower (p less than 0.01 and 0.001, respectively) in the borderline hypertensive group. These findings suggest that borderline hypertension may be maintained by inappropriately increased cardiovascular response to norepinephrine and angiotensin II in the presence of normal sympathetic and renin activity and a normal body sodium-volume state.

Hyperkalemic distal renal tubular acidosis associated with obstructive uropathy

We studied renal function in 13 patients with obstructive uropathy and hyperkalemic metabolic acidosis to characterize the pathogenesis of this disorder. Base-line fractional potassium excretion was lower in all patients than in controls with similar glomerular filtration rates. Acetazolamide was given to 11 patients but failed to increase fractional potassium excretion to normal. In five patients, impaired potassium excretion was associated with decreased ammonium excretion, a urinary pH below 5.5 (5.18 +/- 0.07, mean +/- S.E.M.), and aldosterone deficiency. In the remaining eight patients, the urinary pH did not fall below 5.5 (6.4 +/- 0.2) with acidosis, and we failed to lower the urinary pH and increase fractional potassium excretion to normal by administering a mineralocorticoid and sodium sulfate. A syndrome of hyperkalemic distal renal tubular acidosis may occur in patients with obstructive uropathy. In some patients, this syndrome results from a defect in hydrogen and potassium secretion in the distal nephron rather than from aldosterone deficiency. Obstructive uropathy should be included in the differential diagnosis of hyperkalemic acidosis and renal insufficiency.

Measurement of urine electrolytes: clinical significance and methods

There are specific clinical settings in which each of the urine electrolytes may be diagnostically useful. The urine sodium alone is not efficient in differentiating prerenal azotemia from acute tubular necrosis, but if urine sodium is coupled with some measure of the renal concentrating ability, e.g., the urine:plasma creatinine ratio. discrimination between these two conditions is much improved. Usefulness of the urine sodium in other settings (evaluation of hyponatremia, prediction of acute rejection in renal transplant recipients, index of salt balance) is controversial. Urine potassium may be useful in the evaluation of hypokalemia of obscure etiology and, occasionally, in the form of the urinary Na/K ratio, as a guide to diuretic therapy. Urine chloride is assuming importance in the differential diagnosis of metabolic alkalosis, particularly when Bartter's syndrome is a consideration.

Plasma norepinephrine in essential hypertension. A study of the studies

Of 32 studies comparing plasma norepinephrine concentrations in hypertensive and normotensive groups, 28 (88%) reported higher levels in the hypertensive group. However, only 13 (41%) of the studies reported statistically significant hypertensive-normotensive differences in norepinephrine, leading the present attempt to identify factors differentiating "positive" studies (those reporting significant hypertensive-normotensive differences) from "negative" studies (those reporting nonsignificant differences). Hypertensive norepinephrine levels were similar in positive and negative studies (281 vs 288 pg/ml), but normotensive levels were lower in the positive studies (177 vs 269 pg/ml). When compared with the fluorimetric technique, the radioenzymatic type of assay was associated both with a lower frequency of positive results (25% vs 100%) and greater intrastudy standard deviations (152 vs 72 pg/ml). Hypertensive-normotensive differences varied inversely with age (r = -0.37). Resolution of the persisting controversy about norepinephrine levels in essential hypertension will require more attention to the causes of variability associated with the assay technique, to the sources, characteristics, and treatment of the normotensive controls, and to the age of the patient population.

Chronic treatment with the new potent vasodilator Ro 12-4713 in moderate to severe hypertension: effects on blood pressure, endocrine function, sodium and plasma volume

The antihypertensive efficacy and endocrine profile of the new antihypertensive agent, Ro 12-4713, were evaluated in 23 patients (17 men and 6 women) with moderate to severe arterial hypertension. Following addition of Ro 12-4713 to pre-existing therapy with diuretics and beta-blockers or sympatholytics, blood pressure in most of the patients was normalized within one month by a daily dose of 60 to 120 mg. Heart rate was only slightly increased. Orthostatic hypotension was not observed. Weight gain or oedema formation occurred in 14 patients within the first four weeks, but could be controlled satisfactorily by intensified diuretic therapy. Increased hair growth occurred in most of the patients. After a mean duration of treatment of 2.8 months, plasma volume and plasma and urine sodium were unaltered, and plasma potassium was slightly decreased. Plasma renin activity was doubled, whereas plasma aldosterone concentrations were unaltered. Plasma norepinephrine levels were high before and increased only slightly during chronic Ro 12-4713 treatment, whereas urinary norepinephrine excretion was unchanged. Plasma and urinary epinephrine were unaltered by Ro 12-4713. Ro 12-4713 appears to be a potent vasodilator for the combination treatment of hypertension in men.

Norepinephrine clearance and pressor effect in normal and hypertensive man

Whether and to what extent the sympathetic nervous system participates in the development of essential hypertension has remained largely unclear. The role of the adrenergic effector - cardiovascular response axis in the pathogenesis of essential hypertension was investigated by combined analysis of blood levels, total plasma clearance and cardiovascular pressor effects of norepinephrine (NE). Measurements of plasma NE and blood pressure were performed before, during and after an intravenous infusion of NE at stepwise increasing rates in approximately age and sex-matched groups of 28 normal subjects and 35 patients with essential hypertension. The threshold of the pressor effect of NE was lower in hypertensive than in normal subjects (20 +/- 10 vs. 42 +/- 26 ng/kg min; P < 0.001); but the slope of the dose - resonse curve and basal endogenous plasma NE were in the average similar. Total plasma NE clearance estimated under steady state conditions was similar in normal and hypertensive subjects (5.3 +/- 2.5 vs. 5.4 +/- 2.31/min). NE clearance corrleated inversely with basal plasma NE in normal subjects (r = 0.57; P < 0.005). The plasma half-life of NE was about 2 min. These findings demonstrate that basal blood levels and total plasma clearance of NE during NE infusion are usually normal in essential hypertension. A low threshold of the pressor effect of NE in the presence of normal adrenergic activity may contribute to the development and/or maintenance of essential hypertension.

Age-rated profile of cardiovascular reactivity to norepinephrine and angiotensin II in normal and hypertensive man

The interrelationships among age, cardiovascular pressor reactivity to intravenously infused norepinephrine (NE) or angiotensin II, and endogenous plasma NE or renin (PRA) levels were evaluated i 31 normal subjects and 37 patients with essential hypertension. In normal subjects both angiotensin II pressor dose and PRA decreased progressively with aging. Angiotensin pressor dose correlated positively with PRA (r = 0.41, P < 0.025) and inversely with age (r = -0.46, P < 0.02). NE pressor dose and basal plasma NE were also positively correlated (r = 0.53, P < 0.005), but the two factors remained largely unchanged with aging. Findings in essential hypertension differed in certain aspects. Angiotensin II pressor dose did not correlate with either basal PRA or age; and pressor doses of NE and angiotensin II tended to be lower in some patients than in normal subjects. These findings indicate that aging is accompanied by a physiologic increase in cardiovascular reactivity to angiotensin II, probably due to a concomitant decrease in circulating renin. The dissociation between angiotensin pressor dose and PRA in essential hypertension suggests an interference from an other factor.

Recent pathogenic aspects in essential hypertension and hypertension associated with diabetes mellitus

The sympathetic system, the body sodium-fluid volume state, the renin-angiotensin system, functional and structural characteristics of the heart and blood vessels, and some other components are important complementary factors in blood pressure regulation. A deviation from the normal equilibrium among these components, with a persisting non-physiologic increase in pressor factor(s) or in the basal vascular tone and/or cardiovascular reactivity to pressor factors, leads to hypertension. This review discusses recent observations and concepts regarding the pathogenesis of essential hypertension and hypertension associated with diabetes mellitus. It focuses on the roles of various pressor factors as well as cardiovascular pressor responsiveness in the genesis of high blood pressure and in the antihypertensive mechanism of diuretic treatment.

Effects of short-term norepinephrine infusion on plasma catecholamines, renin, and aldosterone in normal and hypertensive man

The acute responsiveness of plasma catecholamine, renin (PRA), and aldosterone levels to exogenous norepinephrine was studied under placebo conditions and following renin (PRA), and aldosterone levels to exogenous norepinephrine was studied under placebo conditions and following renin-angiotensin activation by diuretic pretreatment in 25 normal subjects and 34 patients with borderline-to-moderate essential hypertension. Norepinephrine infusion caused increases in plasma norepinephrine (PNE) that correlated with the infused norepinephrine dose (p < 0.001); this relationship was similar in normal and hypertensive subjects and unaltered by diuretic therapy. Plasma epinephrine and dopamine levels were unchanged during norepinephrine infusion. Norepinephrine infusion at pressor doses stimulated PRA (p < 0.01). The PRA responses correlated with the dose of infused norepinephrine (p < 0.0025), and norepinephrine-stimulated PRA correlated with basal PRA (p < 0.001). These norepinephrine-PRA relationships were unaltered by diuretic treatment and similar in normal and hypertensive subjects. In both groups, norepinephrine also caused a similar increase in plasma aldosterone (p < 0.05) under placebo conditions, but not following diuretic therapy. These findings demonstrate that an acute increase in the blood levels of the adrenergic neurotransmittor, norepinephrine, causes mild but distinct stimulation of plasma renin and aldosterone levels. Renin release in response to exogenous norepinephrine is not enhanced following renin-angiotensin activation by diuretic pretreatment. The responsiveness of the renin-angiotensin-aldosterone system to an acute norepinephrine input seems to be intact in essential hypertension.

Factors determining direct arterial pressure and its variability in hypertensive man

Intra-arterial pressure was recorded continuously in 26 patients with uncomplicated essential hypertension under standardized conditions. Recordings were analyzed beat by beat to obtain mean pressures and variability, expressed as the standard deviation of the frequency histogram. The major factors influencing variability were the level of pressure and the intensity of physical activity; systolic variability increased with progressive impairment of sino-aortic baroreflexes. Diastolic pressure increased with the level of sympathetic activity as reflected by plasma norepinephrine levels. After allowance for the decrease of plasma renin activity (PRA) with age, direct relationships were observed between PRA (log values) and the level of pressure and systolic variability; plasma angiotensin II values did not correlate. Systolic variability increased with the systolic response to cold but was unrelated to the response to dynamic or isometric exercise. Variability also tended to increase with obesity and was unrelated to age, sex, or race.

Effects of chronic alpha and beta adrenoceptor blockade with labetalol on plasma catecholamines and renal function in hypertension

Plasma catecholamines and renal function were evaluated in 18 patients with essential hypertension treated with the alpha and beta adrenoceptor blocking agent, labetalol. Following 6 weeks of labetalol therapy, blood levels of epinephrine and norepinephrine remained unaltered. Glomerular filtration rate and renal plasma flow were decreased similarly by about 20% (P less than 0.025). Tubular rejection fraction of sodium was increased by 36% (P less than 0.001) while sodium excretion was comparable to control conditions. Labetalol's potential to cause a mild reduction in kidney function should be considered, but may have no clinical consequences in most hypertensive patients receiving such treatment. The lack of increased plasma catecholamine levels during therapy supports the concept that labetalol's alpha-blocking potential is limited to post-junctional receptors, leaving the prejunctional feedback control of catecholamine release intact. Moreover, labetalol's blood pressure-lowering mechanism may be largely independent of changes in sympathetic nervous activity.

Prevalence, pathogenesis, and functional significance of aldosterone deficiency in hyperkalemic patients with chronic renal insufficiency

Our findings indicate that hypoaldosteronism occurs commonly (23/31 patients) in hyperkalemic patients with chronic renal insufficiency and that the deficiency of aldosterone contributes to the pathogenesis of the hyperkalemia. In most patients (83%), hypoaldosteronism could be accounted for by deficient renal secretion of renin, but in some patients (17%) overt renin deficiency did not appear to be present, and therefore other (unidentified) causes of aldosterone deficiency must be invoked. The results also indicate that the urinary excretion rate of aldosterone secretion rate in this group of patients.