Extended-release felodipine in patients with mild to moderate hypertension. Felodipine ER Dose-Response Study Group

Two hundred eighty-six patients with mild to moderate hypertension who had untreated diastolic blood pressure while seated of 95 to 115 mm Hg were randomized to receive placebo or once-daily doses of 2.5, 5, or 10 mg of the dihydropyridine calcium channel blocker felodipine extended release (ER). Blood pressure was measured 24 hours after dosing (at trough). Mean reductions in diastolic blood pressure after 8 weeks of double-blind treatment were significantly greater in each of the ER felodipine treatment groups (2.5, 5, and 10 mg ER felodipine: -7.8, -9.5, and -11.3 mm Hg, respectively) than in the placebo group (-5.3 mm Hg). The effect was dose dependent for both diastolic and systolic blood pressure. Moreover, much of the peak antihypertensive effect was still present at trough, confirming the 24-hour efficacy of the drug. Felodipine was well tolerated.

Characterization of a low molecular weight Na-K-ATPase inhibitor of urinary origin

It has been demonstrated that expansion of extracellular fluid volume induces the release of a low-molecular-weight natriuretic and sodium-potassium-activated adenosine triphosphatase inhibiting hormone (NKAI). In this study, we used a highly purified hormone extracted from pooled hypertensive urines (u-NKAI). Like ouabain, this compound was found to be a potent inhibitor of the sodium-potassium-activated adenosine-triphosphatase and potassium-stimulated paranitrophenyl phosphatase enzyme systems as well as a vasoconstrictor in vitro. In contrast to ouabain, which is a competitive inhibitor of both enzyme systems with respect to potassium, u-NKAI is noncompetitive. Furthermore, u-NKAI differs from ouabain by its lack of cross-reactivity with digoxin antibodies. In addition, whereas ouabain binds to both high-affinity and low-affinity binding sites on the sodium-potassium-activated adenosine-triphosphatase enzyme in the absence of potassium, u-NKAI binds only to the low-affinity binding sites. This study demonstrates that the highly purified u-NKAI, although ouabain-like in certain respects, is not an "endogenous ouabain."

Controversies in the diagnosis and treatment of hypertension: a personal review of JNC V

In January 1993 the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure published its fifth report (JNC V). The report highlighted the importance of systolic hypertension and recommended that hypertension should be diagnosed--regardless of age--when systolic blood pressure readings are consistently > or = 140 mm Hg. JNC V reflected the opinion in JNC IV that several drug classes--including diuretics, beta blockers, angiotensin-converting enzyme (ACE) inhibitors, calcium antagonists, and alpha blockers--are suitable for initiating antihypertensive therapy. However, JNC V gave preference to diuretics and beta blockers because these drug classes have been shown to reduce the incidence of stroke and cardiovascular events in clinical trials; similar studies with the newer drug classes have not yet been completed. This recommendation is highly controversial because the benefits of diuretic and beta-blocker use are most evident in the elderly, and the beneficial effects of these drugs on the incidence of coronary events are relatively modest. Further, growing experience with ACE inhibitors and calcium antagonists shows that these agents lack the metabolic disadvantages of older agents and can exhibit antiatherosclerotic and antihypertrophic vasoactivity. Although to date the clinical benefits of the newer agents have been documented in conditions other than hypertension, the data are persuasive and indicate a probability that these drugs will improve prognosis in hypertensive patients. JNC V also emphasized lifestyle modifications; however, even when they decrease blood pressure, dietary and other nonpharmacologic strategies have not been shown to lower the incidence of clinical events.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic characteristics of hypertension: importance of positive family history

This study was performed to compare metabolic and endocrine characteristics of untreated hypertensive patients and normal controls. Measurements were made in age-matched, body mass index (BMI) matched, normotensive patients with (n = 40; age = 53; BMI = 28) and without (n = 39; age = 54; BMI = 27) a family history of hypertension and hypertensive patients with (n = 38; age = 53; BMI = 28) and without (n = 25; age = 54; BMI = 29) a family history of hypertension. Norepinephrine, renin activity, and total cholesterol blood concentrations were similar in normotensive patients with a positive family history of hypertension and in hypertensive patients with or without a family history. Similarly, there were no differences in plasma insulin concentrations or insulin/glucose ratios between the normotensive patients with a family history of hypertension and hypertensive patients with or without a family history. But in all three groups the values were significantly greater (at least p < 0.05 for each) than in the normotensive patients without a family history. Increases in systolic blood pressure during treadmill testing were 51 +/- 4 mm Hg in the normotensive patients with a family history, 50 +/- 3 mm Hg in hypertensives with a family history, and 45 +/- 5 mm Hg in hypertensives without a family history; these changes were all less (p < 0.05 for each) than in normotensives without a family history (65 +/- 3 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Possible novel action of ouabain: allosteric modulation of vascular serotonergic (5-HT2) and angiotensinergic (AT1) receptors

Experiments were carried out to determine the effects of ouabain and dihydroouabain, both at 10 microM, on the vasoconstrictor responses of isolated rabbit blood vessel rings to both serotonin and angiotensin II. Ouabain plus dihydroouabain increased the sensitivity of central ear artery to serotonin and markedly reduced the antagonist potency of 0.1 microM prazosin against serotonin in this blood vessel; dihydroouabain alone had no effect. Ouabain, markedly reversed the reduction of maximal contractile response by both 2-brom-d-lysergic acid diethylamide against serotonin in aorta and 2-n-propyl-4-trifluoromethyl-1-[(2'-1H-tetrazol-5yl)biphenyl -4- yl)methyl]imidazole-5-carboxylic acid (EXP 3892) against angiotensin II in femoral artery; dihydroouabain had no effect. Whereas both 10 microM ouabain and dihydroouabain produced nearly maximal inhibition of Na+K+ATPase, dihydroouabain failed to modulate the vasoconstrictor responses to either serotonin or angiotensin II. Thus, it is concluded that the vasoconstrictor modulatory effects of ouabain are mediated by mechanisms unrelated to Na+K+ATPase inhibition. The present results are consistent with the hypothesis that both 5-hydroxytryptamine2 and angiotensinergic receptors can exist in high and low activity states. It is proposed that 5-hydroxytryptamine2 receptors exist in a low activity state in the ear artery, or are converted to the low activity state by 2-brom-d-lysergic acid diethylamide in the aorta. Hypothetically, 2-n-propyl-4-trifluoromethyl-1- [(2'-(1H-tetrazol-5yl)biphenyl-4-yl)methyl]imidazole-5-carbo xylic acid also converted the angiotensinergic receptor to the low activity state in femoral artery. In all three cases, ouabain enhanced vasoconstriction to serotonin and angiotensin II, respectively, possibly by allosterically modulating the respective receptors in these vessels to their high activity states.

Lead-induced hypertension: possible role of endothelial factors

The results of this study confirm that low lead (0.01%) but not high lead (0.5%) administration results in increased blood pressure in rats treated for up to 12 months. This effect appeared to be related to an imbalance of endothelially-derived vasoconstrictor and vasodilator compounds in low lead-treated animals but not in high lead-treated animals. In low lead-treated rats, measurement of plasma endothelins 1 and 3 (ET-1 and ET-3) revealed that ET-3 concentration increased significantly after both 3 months (Experimental, 92.1 +/- 9.7 v Control, 46.7 +/- 12.0 pmol/mL; P < .001) and 12 months (Experimental, 105.0 +/- 9.3 v Control, 94.1 +/- 5.0 pmol/mL; P < .01) while ET-1 was unaffected. Plasma and urinary cGMP concentrations (as a reflection of endothelium-derived relaxing factor (EDRF)) decreased significantly at 3 months (plasma, Experimental, 1.8 +/- 0.9 v Control, 4.2 +/- 1.6 pmol/mL; P < .001) and 12 months (plasma, Experimental, 2.2 +/- 0.7 v Control, 4.2 +/- 0.9 pmol/mL; P < .001). Thus, the path to development of hypertension in low lead rats may be through an increase in the concentration of the vasoconstrictor hormone, ET-3, and a decrease in the vasodilator hormone, EDRF. High levels of lead exposure did not result in hypertension, perhaps because plasma concentrations of ET-1, ET-3 and cGMP were unaltered at 3 months, while ET-1, ET-3 and cGMP concentrations were coordinately and significantly decreased at 12 months.

Predominance of high molecular weight plasma Na(+)-K(+)-ATPase inhibitor in essential hypertension

Circulating inhibitors of the transport enzyme, sodium-potassium-activated adenosine triphosphatase (Na(+)-K(+)-ATPase), have been shown to be of possible pathogenetic importance in the mechanism of essential hypertension. Although previous studies have demonstrated the presence of both high molecular weight (HMW) and low molecular weight (LMW) natriuretic plasma Na(+)-K(+)-ATPase inhibitors, no previous attempts have been made to ascertain whether HMW or LMW forms predominate in hypertension. In this study, plasma samples obtained from 26 patients with essential hypertension, 12 normotensive controls, and six normotensives with a family history of hypertension, were separated into HMW and LMW moieties by passage through a 1 kDa Amicon membrane. The LMW moiety was separated on C18 Sep-Pak cartridges, applying a 10% step-wise acetonitrile trifluoroacetic acid gradient. The HMW moiety was further separated on Sephadex G-75. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed that the fraction with inhibitory activity contained a distinct 12 kDa protein band, with staining intensity depending on the presence or absence of hypertension. Na(+)-K(+)-ATPase inhibitory activity was found in several LMW fractions, but differences between hypertensives and normotensives were observed in only one fraction (0.29 +/- 0.12 SD v 0.11 +/- .12 mumol/L ouabain equivalents, P < .01). Na(+)-K(+)-ATPase inhibitory activity in the HMW fraction was 38 x the inhibitory activity in the LMW fraction and was significantly increased in hypertensives as compared to normotensive controls (10.9 +/- 8.9 v 1.3 +/- 0.8 mumol/L ouabain equivalents, P < .01). Inhibitory activity in both HMW and LMW fractions correlated positively with mean blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Coagulation and inhibitory and fibrinolytic proteins in essential hypertension

Arterial hypertension (HTN) increases the risk of cerebral coronary, and other vascular complications that frequently involve platelet activation and blood coagulation. Several key proteins in the blood coagulation, fibrinolytic and inhibitory systems were studied in 29 men with HTN (aged 45 +/- 3 yr) and 15 normal men of the same age. Plasma levels of high-molecular-weight kininogen and factors XII, IX, VII, X, II, and XIII, as well as von Willebrand factor (vWF), fibrinogen, fibronectin, alpha 2-antiplasmin, tissue-plasminogen activator, D-dimer, platelet factor-4, and protein C were measured by the use of appropriate functional and immunologic assays before and after a cardiopulmonary exercise stress test. The concentrations of vWF, alpha 2-antiplasmin, and D-dimer were significantly (P < 0.02) higher in the HTN group as compared with the control group. The exercise stress test resulted in significant rises in the plasma vWF, alpha 2-antiplasmin, and tissue-plasminogen activator levels in the two groups. The concentrations of vWF and D-dimer were related to diastolic blood pressure (r = 0.44 and 0.40, respectively; P < 0.02). Levels of vWF also were related to left ventricular mass index and left ventricular posterior wall and septal thickness (r = 0.34, 0.43, and 0.34, respectively; P < 0.05). The constellation of these findings suggests a low-grade fibrin formation and degradation, the magnitude of which is related to the diastolic blood pressure. The observed abnormalities can potentially contribute to the cardiovascular complications of untreated HTN.

Sustained-release nicardipine in mild-to-moderate hypertension

STUDY OBJECTIVE

To evaluate the antihypertensive effects and tolerability of a sustained release preparation of nicardipine (NIC SR), a dihydropyridine calcium channel antagonist.

DESIGN AND INTERVENTIONS

After at least 1 week without receiving antihypertensive medications and 2 weeks of single-blind placebo treatment, the patients were randomized to receive in a double-blind fashion, either placebo or NIC SR 30, 45, or 60 mg twice daily at 12-h intervals for 12 weeks. Supine and standing blood pressure were measured in all patients and 24-h ambulatory blood pressure monitoring was performed in a subset of 75 patients at baseline during treatment with single-blind placebo and during the double-blind treatment period.

SETTING

Academic and private hypertension research clinics.

PATIENTS

Two hundred sixty-four patients with supine diastolic blood pressures of 95 to 114 mm Hg, ranging in age from 22 to 75 years and in weight from 50 to 137 kg, approximately evenly divided by gender; one third were black.

RESULTS

In comparison with placebo, all doses of NIC SR significantly reduced systolic and diastolic blood pressures, with a trend toward greater effects from 45 to 60 mg twice daily than with 30 mg twice daily. At all doses, reduction of blood pressure from baseline levels was fully apparent within the first 2 weeks of therapy and was maintained throughout the remaining 10 weeks of the trial. Ambulatory blood pressure monitoring demonstrated that the antihypertensive effect was maintained throughout the dosing interval. Adverse effects were primarily extensions of pharmacologic activity (eg, pedal edema, flushing). Six percent of the placebo group and 10 percent of the combined NIC SR groups experienced at least one adverse event that was judged to be probably related to therapy. Withdrawals due to unacceptably high blood pressure totaled 5 percent of the combined NIC SR groups and 25 percent of the placebo group.

CONCLUSIONS

Sustained-release nicardipine at a dose of 30 to 60 mg every 12 h provided effective and generally well-tolerated antihypertensive control throughout the day in most patients with mild-to-moderate essential hypertension.

Comparison of bisoprolol with atenolol for systemic hypertension in four population groups (young, old, black and nonblack) using ambulatory blood pressure monitoring. Bisoprolol Investigators Group

The antihypertensive effects of drugs are partly determined by characteristics of the patients treated. A randomized, double-blind study used 24-hour ambulatory blood pressure (BP) monitoring to compare the effects of 2 beta blockers, bisoprolol (10 to 20 mg; n = 107) and atenolol (50 to 100 mg; n = 96), administered once daily in 4 population groups. After a 4-week placebo period, patients with an office diastolic BP between 95 and 114 mm Hg were stratified according to race and age, and were randomly assigned to treatment with bisoprolol or atenolol for 8 weeks. BP averages measured by automated monitoring for the 24-hour periods were compared between groups. In elderly patients, the reductions in both average 24-hour systolic and diastolic BP were greater with bisoprolol than with atenolol (13 +/- 3/13 +/- 1 mm Hg [n = 23] vs 4 +/- 2/6 +/- 1 mm Hg [n = 30]; p < 0.01). Similarly, bisoprolol produced greater reductions in average 24-hour diastolic BP than did atenolol in nonblack patients (16 +/- 2/12 +/- 1 mm Hg [n = 85] vs 12 +/- 2/9 +/- 1 mm Hg [n = 83]; p = 0.02). Bisoprolol and atenolol were similar in the black (10 +/- 5/9 +/- 3 mm Hg [n = 22] and 10 +/- 6/6 +/- 3 mm Hg [n = 13], respectively) and young (15 +/- 1/11 +/- 1 mm Hg [n = 84] and 16 +/- 2/10 +/- 1 mm Hg [n = 66], respectively) groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive treatment with a dual-acting beta-blocker in the elderly

Risk factors in elderly hypertensives: Recent large-scale clinical trials have shown that antihypertensive treatment in the elderly produces meaningful reductions in strokes and other cardiovascular events. However, the treatment of hypertension in older patients is often complicated by the presence of concomitant disorders. Clinical and silent myocardial ischemia, as well as left ventricular hypertrophy and both systolic and diastolic left ventricular dysfunction, frequently coexist with hypertension. Additional clinical considerations in elderly hypertensives include a high prevalence of abnormal lipid and glucose metabolism and a tendency toward decreased renal function. Effects of different antihypertensive drugs: Although diuretics and conventional beta-blockers have been used as first-line drugs in the major clinical trials, some of their effects on metabolic parameters and on the myocardium can make them inappropriate in some patients. Newer drug classes, including angiotensin converting enzyme (ACE) inhibitors, calcium-channel blockers and, more recently, alpha 1-adrenergic blockers are effective alternatives. Dual-acting beta-blockers offer an important new approach for treating hypertension in elderly patients. Effects of carvedilol: Carvedilol possesses both beta- and alpha 1-blocking activity and appears to exhibit calcium channel blocking activity in animals. The alpha 1-blocking properties of this drug help to produce a desirable hemodynamic profile and facilitate appropriate blood pressure and heart rate responses to exercise. Carvedilol does not appear to adversely affect left ventricular systolic function and, in selected patients with heart failure, has been shown to increase the ejection fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertension as a risk factor syndrome: therapeutic implications

Reduction of blood pressure as the only therapeutic goal of antihypertensive treatment may no longer be appropriate. High blood pressure is associated with an increased risk of cardiovascular events, but clinical trials of antihypertensive therapy have shown an inconsistent reduction in major cardiovascular endpoints. Importantly, the incidence of coronary artery disease has been reduced to only a small extent, suggesting that factors beyond high blood pressure are important in the genesis of atherosclerotic disease in hypertensive patients. It is evident, for example, that patients with hypertension have an exaggerated vulnerability to the consequences of lipid abnormalities. Moreover, it has recently been established that hypertension is characterized by insulin resistance and altered glucose tolerance. As a result, high plasma concentrations of insulin produce proliferative effects on vascular smooth muscle and connective tissue, and they may adversely affect the lipid profile. The left ventricle is also involved in hypertension, independent of blood pressure. There is growing evidence that there are increases in the muscle mass of the left ventricle and changes in its diastolic filling characteristics at very early stages of hypertension. The arterial circulation is similarly involved, for alterations in structure or function (reflected by diminished arterial compliance) can be demonstrated prior to the appearance of clinical hypertension. New therapeutic strategies should be aimed at the full spectrum of hypertension-related changes. Because the renin-angiotensin system can contribute to the structural and functional cardiovascular characteristics of this condition, such agents as angiotensin-converting enzyme inhibitors may be especially effective in preventing or reversing these abnormalities and are emerging as a treatment of choice for hypertension.

Application of ambulatory blood pressure monitoring in differentiating between antihypertensive agents

PURPOSE

This multicenter, double-blind, parallel group study assessed the usefulness of the ambulatory blood pressure monitoring (ABPM) technique in differentiating between the once-daily administration of the beta blockers bisoprolol (10 to 20 mg) and atenolol (50 to 100 mg) in terms of efficacy and duration of action.

PATIENTS AND METHODS

The study population consisted of 659 patients with essential hypertension and an average office diastolic blood pressure (BP) between 95 and 115 mm Hg after 4 weeks of placebo treatment. Office BPs were recorded at the end of the 24-hour dosing interval (trough). ABPM was performed in 11 of the 28 institutions participating in this study in a total of 203 patients. These procedures were performed at the end of the placebo phase and again after 8 weeks of active treatment.

RESULTS

With the use of conventionally measured office BPs, the two drugs significantly (p < 0.001) decreased trough systolic and diastolic BPs to a similar extent. By 24-hour monitoring, bisoprolol demonstrated a 33% greater reduction in whole-day average diastolic BP than did atenolol (11.6 +/- 0.7 mm Hg versus 8.7 +/- 0.8 mm Hg, p < 0.01). Significant treatment differences in systolic (p < 0.05) and diastolic (p < 0.01) BPs were also noted for bisoprolol compared with atenolol during the final 4 hours of the dosing interval (-13.2 +/- 1.5/-10.9 +/- 1.0 mm Hg versus -8.9 +/- 1.6/-7.3 +/- 1.1 mm Hg, respectively), and over the time period 6:00 AM to noon (-14.2 +/- 1.3/-11.5 +/- 0.9 mm Hg versus -9.9 +/- 1.4/-7.7 +/- 0.9 mm Hg).

CONCLUSIONS

Whereas conventional BP measurements did not detect differences in the antihypertensive effects of the beta blockers bisoprolol and atenolol, ABPM revealed significant treatment differences in both the efficacy and duration of action of these two agents. These findings indicate the power of this technique to discriminate potentially important differences between apparently similar antihypertensive drugs.

The relationship of arterial compliance with endothelial-derived proteins of the hemostatic system

Cardiovascular risk factors associated with hypertension include alterations in arterial compliance and an increased tendency to thrombosis. In this study we examined the relationship between arterial compliance and endothelial derived components of the hemostatic system: von Willebrand factor (vWF) and tissue plasminogen activator (t-PA). Ten males (4 normal and 6 untreated hypertensives, 41 +/- 12 years) were studied. Compliance of proximal (large vessel) and distal (small vessel) arteries was measured by intraarterial pulse wave analysis; left ventricular wall thickness by echocardiography; and vWF and t-PA by immunoassay of plasma obtained before and immediately after maximum treadmill exercise. Baseline t-PA and vWF correlated inversely with distal compliance (r = -0.74, p = 0.01; r = -0.56, p = 0.09). Exercise strengthened the relationship between vWF and both distal compliance (r = -0.56 to r = -0.86) and proximal compliance (r = -0.44 to r = -0.70). Moreover, post-exercise levels of vWF and t-PA were each significantly related to left ventricular posterior wall and septal thickness. Of note, these protein concentrations correlated more strongly with arterial compliance and left ventricular wall thickness than with blood pressure. Thus, arterial compliance and left ventricular wall thickness appear to be more powerful than blood pressure as predictors of the endothelial release of vWF and t-PA in response to exercise. These findings indicate that some of the key cardiac and arterial characteristics of hypertension might be linked to increased endothelial reactivity to hemodynamic stress.

Clinical experience with the angiotensin II receptor antagonist losartan. A preliminary report

The nonpeptide angiotensin II (AII)-receptor antagonist losartan is a selective blocker of the pressor effects of AII. It is now being evaluated as an anti-hypertensive drug in multicenter clinical trials in the United States and other countries. Preliminary inpatient studies have shown that after 5 days of treatment, losartan--in doses of 50, 100, and 150 mg--is significantly more effective than placebo in decreasing blood pressure, and has efficacy similar to that of the angiotensin-converting enzyme (ACE) inhibitor enalapril. Large-scale dose-ranging studies in ambulatory hypertensive patients have shown that 10- and 25-mg losartan doses have brief effects in lowering blood pressure, but when given once daily, 50 mg is the minimal dose needed to produce significant day-long decreases in blood pressure. Interestingly, higher doses do not appear to exhibit greater efficacy; however, the effects of these doses are all similar to those of enalapril (20 mg once daily). Losartan's long duration of action is documented by ratios of trough (end of 24-h dosing interval) to peak antihypertensive effects, which are consistently above 50%. Clinical experiences thus far have indicated a low incidence of adverse events. Preliminary animal and in vitro investigations have shown that losartan produces beneficial effects on cardiac function, renal function, and survival that are similar to those of ACE inhibitors. Additional studies are now under way to define more fully the cardiovascular and metabolic profiles of losartan.

Left ventricular hypertrophy and antihypertensive therapy

Left ventricular hypertrophy is more common in hypertensive individuals than in normotensive persons. Its presence in hypertensive patients is associated with an increased incidence of ventricular arrhythmias, myocardial infarction, congestive heart failure, stroke and cardiovascular mortality. Echocardiography is more sensitive than electrocardiography in detecting left ventricular hypertrophy. Echocardiographic evidence of this condition in patients with borderline hypertension may identify those who need treatment. Weight reduction and drug therapy can prevent or reverse ventricular hypertrophy in hypertensive patients. Recent studies suggest that some antihypertensive drugs are more effective than others in reducing left ventricular hypertrophy. These agents include beta-adrenergic blockers, angiotensin converting enzyme inhibitors, calcium channel blockers and sympatholytic agents. Although little evidence exists to show that reduction of left ventricular mass decreases cardiovascular morbidity and mortality, avoidance of antihypertensive agents that may aggravate hypertrophy would seem prudent.

Heredity and hypertension: impact on metabolic characteristics

This study was performed to evaluate the possible role of heredity in the clinical characteristics of hypertension. Metabolic, endocrine, and renal measurements were compared in subjects with normal blood pressure who had a family history of hypertension (n = 60) with those of subjects with normal blood pressure who did not have a family history of hypertension (n = 48). The groups were matched for age (mean, 44 +/- 2 years and 45 +/- 2 years) and blood pressure (127 +/- 1/77 +/- 1 mm Hg and 127 +/- 2/77 +/- 1 mm Hg). The following parameters were higher in the patients with a family history of hypertension than in those without. Plasma insulin concentrations (14.1 +/- 1.1 vs 10.8 +/- 1.0 microU/ml; p less than 0.05), insulin-glucose ratio (0.15 +/- 0.01 vs 0.11 +/- 0.010; p less than 0.05), norepinephrine concentrations (315 +/- 24 pg/ml vs 208 +/- 20 pg/ml; p less than 0.01), plasma renin activity (2.1 +/- 0.2 ng Angl/ml/hr vs 1.6 +/- 0.2 ng Angl/ml/hr; p less than 0.02), total cholesterol levels (217 +/- 8 mg/dl vs 197 +/- 0.3 mg/dl; p less than 0.05), creatinine clearance (125 +/- 9 ml/min vs 96 +/- 8 ml/min; p less than 0.01), and albumin excretion rate (3.2 +/- 0.3 micrograms/min vs 2.6 +/- 0.3 micrograms/min; p = 0.1). Moreover, patients with a family history of hypertension had smaller increases in systolic blood pressure during treadmill exercise (55 +/- 3 mm Hg vs 64 +/- 3 mm Hg; p less than 0.03). There were no differences in echocardiographic left ventricular mass index between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Norepinephrine amplifies angiotensin II-induced vasoconstriction in rabbit femoral artery

Several reports have focused on the ability of angiotensin II to amplify vascular contractile responses to norepinephrine, but none have determined whether norepinephrine enhances angiotensin II-induced vasoconstriction. Measuring isometric contraction in isolated rabbit femoral artery rings, we have found that the angiotensin II-induced contractile response was amplified in the presence of a threshold contraction to norepinephrine, as manifested by a 2.9-fold leftward shift of the midpoint of the concentration-response curve with no change in the maximal response. This amplification was attenuated markedly by nifedipine (0.1 microM), a calcium channel antagonist, implicating calcium channel activation in the amplification phenomenon. Precontracting the smooth muscle with a threshold concentration of angiotensin II had no enhancing effect on further angiotensin responses, indicating that the norepinephrine-induced amplification was due to a specific action of norepinephrine, rather than to a precontraction itself. In experiments in which the angiotensin II response was diminished by the presence of the noncompetitive angiotensin II antagonist [Sar1 Ala8]angiotensin II (0.3 microM), norepinephrine affected the angiotensin II response primarily by increasing the maximal response attainable. Prazosin (0.1 microM) both blocked the norepinephrine threshold contraction and abolished completely the amplification. However, when the norepinephrine concentration was increased until a threshold contraction was elicited in the presence of a fixed concentration of prazosin, amplification of the angiotensin II response was restored. These results indicate that norepinephrine exerts its amplifying effect on angiotensin II via activation of alpha-1 adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Dependency of arterial compliance on circulating neuroendocrine and metabolic factors in normal subjects

Reduced arterial compliance is now recognized as a feature of hypertension. Similarly, metabolic factors such as insulin, catecholamines and lipids are also associated with hypertension. This study explores the possibility that these neuroendocrine and metabolic factors may separately influence arterial compliance. Proximal compliance (aorta and large arteries) and distal compliance (small arteries and arterioles) were measured in 57 volunteers (30 hypertensive and 27 normotensive subjects, mean age 45 years). Compliance was quantified by analysis of arterial pulse wave contours obtained intraarterially together with hemodynamic estimates. Proximal compliance correlated with plasma insulin (r = -0.49; p less than 0.001), norepinephrine (r = -0.50; p less than 0.002), triglycerides (r = -0.39; p less than 0.01), total cholesterol (r = -0.33; p = 0.02) and high-density lipoprotein cholesterol (HDL) (r = 0.37; p less than 0.02). Similarly, distal compliance correlated with insulin (r = -0.37; p less than 0.02), triglycerides (r = -0.39; p less than 0.01), total cholesterol (r = -0.38; p less than 0.01) and HDL (r = 0.51, p less than 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Circulatory and extracirculatory effects of angiotensin-converting enzyme inhibition

The antihypertensive effects of angiotensin-converting enzyme (ACE) inhibitors cannot be fully explained by their actions on the circulating renin-angiotensin system (RAS). Agents such as captopril or enalapril maintain efficacy during long-term therapy even when plasma concentrations of converting enzyme or angiotensin II are not fully suppressed. Components of the entire RAS exist at several sites, thereby making it possible for drugs to produce effects at extracirculatory locations. An ACE inhibitor such as quinapril that has a comparatively short plasma concentration half-life binds strongly to plasma ACE as well as to ACE in key tissues including artery wall, heart, and kidney. The effects of ACE inhibition on the tissue RAS are of potential importance in fully explaining the blood pressure-lowering effects of these drugs. ACE inhibitors might also reduce blood pressure by blocking nonhemodynamic actions of angiotensin II. They affect vascular properties by increasing compliance of arteries and they act on baroreceptors and central regulatory mechanisms. Furthermore, ACE inhibitors affect other neuroendocrine systems, including aldosterone, kinins, and prostaglandins; attenuation of sympathetic activity can contribute further to their antihypertensive properties. Actions independent of circulating renin effects do not necessarily require plasma ACE inhibition throughout a 24-hour period. Sustained antihypertensive effects by drugs with short durations of plasma ACE inhibition give credibility to therapeutic targets beyond the circulating RAS.

A dose escalation trial comparing the combination of diltiazem SR and hydrochlorothiazide with the monotherapies in patients with essential hypertension

A multicentre, randomised, placebo-controlled parallel group study comparing various doses of the combination diltiazem SR (DTZ SR)/hydrochlorothiazide (HCTZ) with the monotherapies was performed to delineate the optimal antihypertensive dosage of the two drug combinations. The study was carried out in 298 patients with mild to moderate essential hypertension (stable supine diastolic blood pressure, DBP, greater than or equal to 95 and less than or equal to 110 mmHg). After a single-blind placebo lead-in period lasting 4-6 weeks to establish stable baseline BP, the patients were randomised to receive either placebo (n = 75), HCTZ (n = 76), DTZ SR (n = 72), or the combination of DTZ SR/HCTZ (n = 75). There were three 4-week evaluation periods with forced escalation of therapy as follows: HCTZ (6.25, 6.25, 12.5 mg twice daily), DTZ SR (60, 90, 120 mg twice daily), and the combination of DTZ SR/HCTZ (60/6.25, 90/6.25, 120/12.5 mg twice daily). DTZ SR/HCTZ (120/12.5 mg) produced statistically significantly greater reductions in supine DBP compared with each monotherapy and placebo. The lower doses of DTZ SR/HCTZ (60/6.25 mg and 90/6.25 mg) produced statistically significantly greater supine DBP reductions compared with DTZ SR monotherapy and placebo, but not compared with HCTZ monotherapy. A comparison of reduction in supine DBP between evaluation periods demonstrated a dose-response relationship for the combination therapy in reducing BP over the dosage range studied. Adverse clinical and laboratory events were not significantly different between the therapies.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of left ventricular hypertrophy on blood pressure responses to exercise

It is claimed that exaggerated blood pressure (BP) responses to exercise are predictive of future hypertension and may also be indicative of left ventricular (LV) hypertrophy. The relation between LV hypertrophy and maximal exercise BP was examined in 35 normal male volunteers and 65 untreated hypertensive male patients. Multiple stepwise regression analysis revealed that preexercise systolic BP was the major determinant of maximal exercise systolic BP (r = 0.52; p less than or equal to 0.0001), indicating that higher baseline BP predicted higher exercise BP. However, hypertensive patients with LV hypertrophy had the smallest increases in systolic BP with exercise. Accordingly, there was an inverse relation between LV muscle mass and systolic BP responses to exercise in these patients (r = -0.34; p = 0.005). When compared with normotensive subjects, hypertensive patients had lower measures of maximal oxygen uptake and exercise heart rates (p = 0.01). This may indicate lower cardiac performance at maximal exercise and explain the reduced capacity of hypertensive patients with LV hypertrophy to increase systolic BP with exercise. Neither baseline nor exercise BPs correlated with LV mass; instead, the model of regression analysis indicated that body weight was the principal determinant of LV mass. Contrary to previous reports, exaggerated exercise BPs were not associated with LV hypertrophy in hypertensive or normotensive patients.