Blood volume and exchangeable sodium during treatment of hypertension with guanethidine and hydrochlorothiazide

Changes in plasma volume and extracellular fluid volume and after addition of hydralazine to propranolol treatment in patients with hypertension

In 16 patients with hypertension, BP could not be controlled satisfactorily by treatment with propranolol alone (mean dosage 325 mg/day). Plasma volume (PV) (T-1824) and extracellular fluid volume (ECV) (82Br-distribution space) were determined in these patients before and after the addition of hydralazine for three months (mean dosage 135 mg/day). After the addition of hydralazine, PV and ECV increased significantly, by 9% and 3%, respectively. Systolic and diastolic BPs decreased, by 15% and 13%. The mechanisms inducing fluid retention during treatment with hydralazine and the clinical significance of the problem are discussed. It is concluded that the addition of a diuretic to propranolol-hydralazine treatment is often well indicated.

Vasodilatation and sodium retention in prehepatic portal hypertension

Sodium retention and peripheral vasodilatation are common consequences of portal hypertension secondary to cirrhosis. Although peripheral vasodilatation has been extensively documented in prehepatic portal hypertension, it is not known whether sodium retention is also a feature of this entity. The aim of this study in portal vein-constricted rats was to evaluate (a) whether sodium retention is a feature of prehepatic portal hypertension and (b) if sodium retention is present in this model, what its temporal relationship with peripheral vasodilatation might be. It was proposed that an understanding of the temporal interplay between peripheral vasodilatation and sodium retention could shed light on the current theories of sodium retention in portal hypertension. Rats were studied 1, 2, 3, and 4 days after partial portal vein ligation (n = 80) or sham operation (n = 63). Sodium retention was evaluated by changes in the size of the sodium space measured by the volume of distribution of 22Na. Systemic vascular resistance was calculated from mean arterial pressure (measured by arterial catheterization) and cardiac index (measured by thermodilution). A decrease in systemic vascular resistance was already observed on day 1 after constriction of the portal vein (4.2 +/- 0.2 vs. 5.2 +/- 6.1 mm Hg.min.mL-1.100 g; P less than 0.01). However, an expansion of the sodium space, which indicates sodium retention, was not observed until day 2 after induction of portal hypertension (37.1 +/- 0.8 vs. 32.6 +/- 0.7 mL.100 g-1; P less than 0.01). Therefore, sodium retention should be considered along with peripheral vasodilatation among the characteristic features of prehepatic portal hypertension. Because the reduction in systemic vascular resistance preceded the expansion of the sodium space by at least 24 hours, the finding of this study indicates that sodium retention follows peripheral vasodilatation.

Alpha 1-adrenergic blockade and cardiovascular pressor responses in essential hypertension

The effects of selective alpha 1-adrenergic blockade with terazosin on blood pressure and cardiovascular pressor responsiveness were assessed in 17 subjects with mild to moderate essential hypertension (mean age, 48 +/- 2 [SEM] years). As compared with a 2-week placebo period, 8 weeks of terazosin treatment (mean dose, 10.5 +/- 1.7 mg/day) caused a fall of supine (from 153/103 +/- 3/2 to 143/96 +/- 4/2 mm Hg; p less than 0.025) and upright (from 145/106 +/- 4/2 to 131/94 +/- 5/3 mm Hg; p less than 0.01) arterial pressure; a marked blunting of cardiovascular pressor responsiveness to norepinephrine, as judged from the pressor dose (from 73 +/- 9 to 2156 +/- 496 ng/kg/min; p less than 0.02) and from the rightward shift (p less than 0.01) of the plasma concentration-blood pressure response curve; and a slight increase in plasma norepinephrine concentration (from 37.7 +/- 3.3 to 52.2 +/- 7.8 ng/dl; p less than 0.01). Heart rate, body weight, exchangeable sodium, blood volume, and norepinephrine plasma clearance; plasma epinephrine, renin, angiotensin II, and aldosterone levels; the relationships between angiotensin II-induced increases in arterial pressure or plasma aldosterone and the concomitant increments of plasma angiotensin II; and heart rate responsiveness to isoproterenol did not change significantly after terazosin treatment. These findings suggest that the fall of arterial pressure induced by selective alpha 1-adrenergic blockade in subjects with essential hypertension is associated with, and probably explained by, inhibition of alpha 1-mediated, noradrenergic-dependent vasoconstriction. alpha 1-Adrenergic receptor antagonism did not modify body sodium concentration, the adrenomedullary component of the sympathetic nervous system, angiotensin II levels, or beta-adrenergic dependent mechanisms.

Alternative pharmacologic approaches to the initial management of hypertension

Recent clinical trials in hypertension report more deaths due to coronary heart disease in mild hypertensives who received aggressive antihypertensive drug therapy and achieved better blood pressure control. Subset analyses of these trials suggest that diuretic therapy may have contributed to this outcome, possibly through a reduction in serum potassium or an elevation in serum lipids. Because of this, patients with an abnormal pretreatment electrocardiogram, history of myocardial infarction, unstable coronary heart disease, or diuretic-induced hyperlipidemia or hypokalemia unresponsive to management are candidates for alternative antihypertensive agents. A review of the literature suggests that most of the currently available beta-blockers, the alpha 1-antagonist prazosin, the angiotensin-converting enzyme inhibitor captopril, and the vasodilator hydralazine are effective alternatives to thiazide therapy in the initial management of hypertension and are recommended for particular subgroups of patients. Monotherapy with the centrally and peripherally acting sympatholytic agents is not recommended because of the frequent side effects encountered and the inferior hypotensive efficacy reported. Calcium channel blocking agents also appear to be suitable alternatives to thiazides in hypertension, but more experience with these is needed. Alternative pharmacologic agents may be selected on the basis of age, and, to a lesser extent, race.

Causes of inadequate response to antihypertensive drugs. Volume factors

Diuretic therapy, by producing a negative salt and water balance, eliminates the false tolerance to sympatholytic drugs that often occurs during long-term monotherapy. This tolerance results from salt and water retention produced by the drugs. Review of published results suggests a primacy for arterial pressure reduction in this fluid because suppressed renal sympathetic activity should facilitate salt and water excretion through lessened alpha-adrenergic influence on tubular reabsorption, and beta-adrenergic inhibition would diminish renin release thus promoting natriuresis. The return of hypertension that characterizes the false tolerances seems paradoxical because these drugs cause venodilation, which should provide ample storage of expanded blood volume without affecting cardiac output. However, animal studies have suggested that dilated veins have decreased compliance; if that is so, in humans it would mean that fluid retention would be accompanied by a redistribution of blood into the central circulation, with a rise in cardiac output.

Blood pressure, body fluid volumes and glomerular filtration rate during treatment with labetalol in essential hypertension

1 In a single blind study seventeen patients with mild or moderate essential hypertension and normal renal function were treated with labetalol alone in increasing doses from 300 via 600 to 1200 mg daily. 2 Average supine BP (systolic/diastolic) was reduced by 24/19 mm Hg. Seven patients attained a diastolic BP less than or equal to Hg. A significant postural fall in systolic BP was recorded, but no symptomatic orthostatic hypotension occurred. 3 In twelve patients measurements of plasma volume (125I-albumin), extracellular volume (82Br-space) and glomerular filtration rate (51Cr-EDTA clearance) on placebo and subsequently labetalol showed no systemic changes. 4 Side effects were few causing two withdrawals because of impotence and arthralgia. 5 It is concluded that monotherapy with labetalol results in clinically relevant, persistent and dose dependent reduction in BP in patients with mild or moderate essential hypertension, apparently without concomitant expansion of body fluid volumes or influence on glomerular filtration rate.

Changes in plasma volume and extracellular fluid volume after addition of prazosin to propranolol treatment in patients with hypertension

In fifteen patients with hypertension, inadequately controlled during treatment with propranolol alone (mean dosage 333 mg/day), plasma volume (PV) and extracellular fluid volume (ECV) were determined. After addition of prazosin for 3 months (mean dosage 9 mg/day) there was a significant increase in PV and ECV, on average 8 and 5%, respectively. The decrease in supine blood pressure, systolic as well as diastolic, was very modest, on average 11 mmHg (SD +/- 12) and 4 mmHg (SD +/- 7), respectively. The changes in standing blood pressure were more pronounced. It is assumed that the expansion of PV and ECV contributes to the inadequate blood pressure response found in the present study.

The second Lilly Prize Lecture, University of Newcastle, July 1977. beta-Adrenergic receptor blockade in hypertension, past, present and future

All beta-adrenoceptor blocking drugs that have been described share the common property of being competitive inhibitors. They differ in their associated properties, the presence or absence of cardioselectivity, membrane stabilizing activity, and partial agonist activity. Recently some beta-adrenoceptor blocking drugs have been reported which also possess alpha-adrenoceptor blocking activity. The associated properties have been used as a basis for classifying beta-adrenoceptor blocking drugs (Fitzgerald, 1969, 1972). The presence or absence of cardioselectivity is most useful for dividing beta-adrenoceptor blocking drugs. The non-selective drugs (Division I) can be further divided according to the presence or absence of intrinsic sympathomimetic activity (ISA) and membrane stabilizing activity (Fitzgerald's groups I-IV). Group I possess both membrane activity and ISA, e.g. alprenolol, oxprenolol, group II just membrane action, e.g. propanolol, group III ISA but no membrane action, e.g. pindolol. Fitzgerald placed pindolol in group I but should be placed in group III as it possesses a high degree of beta-adrenoceptor blocking potency in relation to its membrane activity (Prichard, 1974). Finally drugs in group IV have neither ISA nor membrane action, e.g. sotalol, timolol. The cardioselective drugs (Division II) can be similarly sub-divided into groups I-IV according to the presence or absence of ISA or membrane action (Fitzgerald grouped all these together as group V). Lastly there are new beta-adrenergic receptor blocking drugs which in addition have alpha- adrenergic receptor blocking properties (Division III).

Failure of methyclothiazide to lower home blood pressure level in "essential" hypertensive and normotensive young men, despite significant plasma volume contraction

Home blood pressure measurements were used to assess the effect of methyclothiazide in young essential hypertensive and normotensive males. Although plasma volume was reduced by approximately 10 percent, blood pressure was not reduced in either group. The lack of effect on blood pressure was probably not attributable to dosage employed, as doubling the dose (5 to 10 mg) in the normal subjects (who were equilibrated on constant diet) did not significantly increase changes in plasma volume, plasma renin activity, aldosterone excretion, urine sodium or blood pressure. The higher dose did result in greater changes in plasma potassium and uric acid. Homeostatic mechanisms which limit the volume mediated and other antihypertensive effects of methyclothiazide apparently achieved complete compensation in these young males. This suggests that thiazide diuretics may not be the drug of first choice in the treatment of hypertension in young adults. Further studies with other diuretics are clearly necessary before the significance of these findings can be fully assessed.

Systemic and renal hemodynamic effects of bupicomide: a new vasodilator

The systemic and renal hemodyanmic effects of bupicomide were studied in 10 male patients with uncomplicated essential hypertension of moderate severity. Bupicomide significantly reduced systolic, diastolic, and mean arterial pressure and peripheral vascular resistance and this hypotensive effect was associated with a reflexive increase in heart rate, left ventricular ejection rate, and cardiac index; it had no effect upon other reflexive sympathetic adjustments induced by upright tilt and the Valsalva maneuver. Bupicomide also increased renal blood flow and decreased renal vascular resistance, but it had no effect upon the glomerular filtration rate. The hypotensive mechanism of bupicomide therefore is mediated by peripheral arteriolar dilation, through vascular smooth muscle relaxation. The more immediate clinical side effects of bupicomide are related to its strong vasodialting action and include headaches, cutaneous flushing, and tachycardia.