Nifedipine and acebutolol in combination for the treatment of moderate to severe essential hypertension

In a randomised, crossover study of patients with moderate to severe essential hypertension, the effects of the calcium entry antagonist nifedipine and the beta-receptor blocking drug acebutolol were studied on their own, and in combination. After 4 weeks of nifedipine tablets 20 mg twice daily (Adalat, Bayer), mean supine blood pressure (BP) fell by 20 mmHg and after 4 weeks of acebutolol 200 mg twice a day (Sectral, May & Baker) by 11 mmHg. When nifedipine and acebutolol were given in combination in the above doses for 4 weeks, there was a significantly greater fall in BP than with either agent alone, supine mean arterial pressure falling by 27 mmHg. The above BPs were measured 2 h after the last dose of tablets. Measurements 12 h after the last dose showed smaller falls in BP, with a significantly greater fall with combination treatment than with acebutolol alone. The fall in BP 12 h after the last dose of the combination was greater than with nifedipine alone but this difference was not statistically significant. This randomised, controlled study showed that nifedipine and acebutolol have a marked additive effect on BP which is sustained for at least 12 h after treatment.

Changes in the plasma levels of atrial natriuretic peptides during mineralocorticoid escape in man

Plasma levels of atrial natriuretic peptide (ANP) were measured by radioimmunoassay in eight normal healthy volunteers before and during mineralocorticoid escape. Mean plasma ANP on a fixed sodium intake before fludrocortisone was 6.5 +/- SEM 1.1 pg/ml. Within 24 h of fludrocortisone administration there was a significant increase in plasma ANP which continued to increase daily reaching a plateau by day 4 (14.9 +/- 2.4 pg/ml) to day 7 (15.1 +/- 2.6 pg/ml). The rise in plasma ANP was closely related to the amount of sodium retained during the fludrocortisone treatment and the sodium 'escape' occurred by days 4 to 7. These results support the concept that ANP could play an important hormonal role in over-coming the sodium-retaining effects of mineralocorticoids in man.

Moderate sodium restriction with angiotensin converting enzyme inhibitor in essential hypertension: a double blind study

Fifteen unselected patients who had essential hypertension and whose average supine blood pressure when they were not receiving any treatment and their usual sodium intake was 162/107 mm Hg were treated with captopril 50 mg twice daily. After one month's treatment their supine blood pressure had decreased to 149/94 mm Hg. They were then instructed to reduce their sodium intake to about 80 mmol(mEq)/day. After two weeks of moderate sodium restriction they were entered into a double blind randomised crossover study comparing the effect of 10 Slow Sodium tablets (100 mmol sodium chloride) with matching placebo tablets while continuing to take captopril and restrict sodium in their diet. After one month of taking placebo their mean supine blood pressure was 137/88 mm Hg with a urinary sodium excretion of 83 mmol/24 h, while after one month of taking Slow Sodium tablets their mean supine blood pressure was 150/97 mm Hg (p less than 0.001) with a sodium excretion of 183 mmol/24 h. The mean supine blood pressure during moderate sodium restriction therefore decreased by 9% and correlated significantly with the reduction in urinary sodium excretion. These results suggest that the combination of treatment with a moderate but practical reduction in sodium intake and an angiotensin converting enzyme inhibitor is effective in decreasing the blood pressure in patients with essential hypertension. This combined approach overcomes some of the objections that have been made to salt restriction alone and to converting enzyme inhibitors alone.

Does oral calcium supplementation lower high blood pressure? A double blind study

Eighteen unselected patients with untreated mild to moderate essential hypertension, whose average supine blood pressure after 2 months' observation on no treatment was 154/103 mmHg, were entered into a double-blind randomized crossover study of 1 month's treatment with calcium lactate gluconate (40 mmol of elemental calcium/day) and treatment with placebo for a further month. Despite a significant increase in total plasma calcium (P less than 0.01) and in 24-h urinary excretion of calcium (P less than 0.025) while taking calcium lactate gluconate, there was no fall in blood pressure with calcium supplementation compared to treatment with placebo.

Plasma immunoreactive atrial natriuretic peptide and changes in dietary sodium intake in man

Plasma levels of immunoreactive atrial natriuretic peptides (IrANP) have been measured in 8 normotensive subjects during alterations in dietary sodium intake. Subjects were studied on their normal sodium intake (2 days) then on a low sodium intake (7 days, 10 mmols Na+/day) and subsequently on a high sodium intake (14 days, 350 mmols Na+/day with the diets being given in a fixed order. Plasma levels (mean +/- S.E.M.) of IrANP on a normal sodium diet were 7.3 +/- 0.9 pg/ml; 4.5 +/- 0.8 on the 7th day of a low sodium intake and 10.8 +/- 1.3; 16.6 +/- 3.3; 15.5 +/- 4.2; 15.6 +/- 2.3 pg/ml respectively or the 1st, 3rd, 10th and 14th day on the high sodium intake. Changes in plasma IrANP were closely associated with changes in urinary sodium excretion. These results suggest that in normal subjects the atrial natriuretic peptides may play an important role in the adaptation to increases in dietary sodium intake both on a short and on a longer term basis.

Validation of beat by beat pulsed Doppler measurements of ascending aortic blood velocity in man

The volume, velocity, and acceleration of ascending aortic blood were measured in man using a pulsed Doppler ultrasound instrument, with online spectral analysis and offline computer processing of velocity data. This system was firstly validated in a test rig capable of generating pulsatile flow of talc particles in water at physiological velocities and accelerations in a model aorta. Doppler measurements correlated well (r greater than or equal to 0.90) with simultaneous electromagnetic measurements of stroke volume, peak ejection velocity, and maximum acceleration in this rig. In vivo validation was performed firstly by comparing simultaneous Doppler and thermodilution cardiac output (Q) measurements; this yielded the following regression equation: Doppler Q = 0.90 X thermodilution Q + 0.03 litre.min-1, r = 0.92; n = 38. Beat by beat measurements were then validated against simultaneous invasive aortic blood velocity measurements made using a Mills electromagnetic cathetertip probe. When paced single beats of different size were compared within subjects the correlation coefficients between Doppler and electromagnetic measurements averaged 0.89 for stroke volume, 0.91 for peak ejection velocity, and 0.79 for maximum acceleration in five subjects. The absolute values for velocity and acceleration from the Doppler system differed significantly from the absolute values given by the electromagnetic system and this difference was not consistent between subjects. It is concluded that the Doppler system can non-invasively record relative changes in left ventricular ejection in man.

Plasma atrial natriuretic peptide: its relationship to changes in sodium intake, plasma renin activity and aldosterone in man

Plasma levels of immunoreactive atrial natriuretic peptide (IrANP), plasma renin activity, aldosterone and vasopressin were measured in 11 normotensive subjects on a low (10 mmol/day), a normal (150 mmol/day) and a high (350 mmol/day) sodium intake. Plasma levels of IrANP increased significantly with increasing dietary sodium intake with levels (means +/- SD) of 3.9 +/- 2.1 pg/ml on the fifth day of the low sodium diet, 6.1 +/- 3.4 pg/ml on the fifth day of the normal sodium diet and 11.4 +/- 4.6 pg/ml on the fifth day of the high sodium diet. Plasma renin activity and aldosterone decreased significantly with increasing sodium intake whereas plasma vasopressin was highest on the high sodium intake. These results suggest that the atrial peptides may be a new and important component in the overall control of sodium and water balance during increased sodium intake.

Effect of increasing calcium intake on urinary sodium excretion in normotensive subjects

Eight normotensive subjects were studied in a randomized crossover trial of a high calcium diet (1800 mg of calcium/day) for a week against a low calcium diet (200 mg of calcium/day) for a further week. The subjects were placed on a diet containing 200 mg of calcium/day throughout the study and the high calcium diet was achieved by supplementing the low calcium diet with calcium glubionate and galactogluconate. Sodium and potassium intake were kept constant throughout the study. Twenty-four hour urinary sodium, potassium, calcium and phosphate were measured daily. In spite of a highly significant increase in calcium excretion from the low to the high calcium diet (P less than 0.0001), there was no increase in sodium or change in potassium excretion with the increased calcium intake. A transient but significant fall in urinary sodium excretion was observed up to the fourth day of the high calcium diet (P = 0.021). Twenty-four hour urinary phosphate excretion fell significantly on the high calcium diet (P less than 0.0001). Body weight, blood pressure, plasma renin activity, aldosterone, plasma creatinine and serum ionized calcium did not change. These results suggest that a short-term increase in calcium intake in normotensive subjects does not increase urinary sodium and potassium excretion.

Changes in plasma immunoreactive atrial natriuretic peptide in response to saline infusion or to alterations in dietary sodium intake in normal subjects

Plasma levels of immunoreactive atrial natriuretic peptide (irANP) have been measured in normal subjects in response to changes in sodium balance induced by either saline infusion or alterations in dietary sodium intake. In eight normotensive subjects, plasma levels of irANP (means +/- s.e.m.) increased from 5.8 +/- 0.9 to 15.8 +/- 4.4 pg/ml plasma after an infusion of isotonic saline (2 litres over a 60-min period). In seven subjects, plasma levels of irANP were measured on the 5th day of a low-sodium diet (10 mmol/day), a normal-sodium diet (150 mmol/day) and a high-sodium diet (350 mmol/day). Plasma levels of irANP increased with increasing sodium intake, with values of 4.0 +/- 0.9 (low-sodium diet), 6.9 +/- 1.3 (normal-sodium intake) and 12.1 +/- 1.8 pg/ml (high-sodium intake). These observations suggest that the atrial natriuretic peptides could be an important hormone system in the control of sodium excretion by the kidney, and thereby of sodium balance in normal man.

Evidence for increased levels of a circulating ouabainlike factor in essential hypertension

The effect of plasma from normotensive and hypertensive subjects on the binding of [3H]ouabain on human erythrocytes was investigated. The binding of [3H]ouabain on human erythrocytes was saturable and highly specific; linear Scatchard plots indicated the presence of a single type of binding site. Human plasma decreased the binding of [3H]ouabain on its receptor to a greater extent than could be accounted for by the plasma potassium concentration. The level of this circulating ouabainlike factor (or factors) was quantitated using a radioreceptor assay. Plasma from 22 hypertensive subjects (systolic blood pressure greater than 160 mm Hg or diastolic blood pressure greater than 90 mm Hg) displayed higher levels than that from 24 normotensive subjects; furthermore there was a positive and significant correlation (r = 0.42, n = 46, p less than 0.004) between the ouabainlike content and the individual subject's systolic blood pressure. The receptor assay described is relatively simple and should be useful for further work on the nature and clinical importance of the endogenous ouabainlike factor.

Raised circulating levels of atrial natriuretic peptides in essential hypertension

Plasma levels (mean +/- SD) of immunoreactive atrial natriuretic peptides (ANP) were significantly higher in 28 hypertensive subjects (17.1 +/- 13.8 pg/ml) than in 24 normotensive subjects (8.4 +/- 3.7 pg/ml) matched as far as possible for age, sex, and race. All subjects were studied on their normal dietary sodium intake. In the normotensive subjects ANP levels were significantly correlated with age but not with blood pressure, whereas in the hypertensive subjects ANP levels were significantly correlated with systolic blood pressure but not with age. These findings may indicate a compensatory reaction to a diminished renal capacity for sodium excretion, in response to increasing age in normotensive subjects and to higher blood pressure in hypertensive subjects.

Effects of changes in dietary sodium intake and saline infusion on immunoreactive atrial natriuretic peptide in human plasma

Plasma levels of immunoreactive atrial natriuretic peptide (IrANP) were measured in healthy normotensive subjects before and after saline infusion and changes in dietary salt intakes. When 2 litres of 0.9% saline (308 mmol Na+) were infused over 1 h, plasma levels (mean +/- SD) of IrANP increased from 5.8 +/- 2.8 pg/ml to 15.8 +/- 12.5 pg/ml. Plasma levels on the fifth day of a low sodium diet (10 mmol/day) were 3.8 +/- 2.4 pg/ml, a normal sodium intake (150 mmol/day) 6.4 +/- 2.9 pg/ml, and a high salt intake (350 mmol/day) 12.7 +/- 6 pg/ml. These results suggest that atrial natriuretic peptides could be important hormones in the control of sodium balance in normal man.

The renin-angiotensin-aldosterone system in decompensated cirrhosis: its activity in relation to sodium balance

Plasma renin activity (PRA), plasma renin concentration (PRC), plasma angiotensin II concentration (AII), plasma and urinary aldosterone (PA, UA) and urinary sodium excretion (UNaV) were measured in 51 normal controls, 16 patients with decompensated cirrhosis (i.e. ascites and/or oedema present) in sodium equilibrium (Group 1) and 13 patients with decompensated cirrhosis in a phase of active sodium retention (Group 2). In Group 1 the mean supine and erect values, although lower, were not significantly different from controls. In Group 2 the mean values were significantly elevated, but several individual values were within the normal range; there were significant direct relationships between plasma renin activity and plasma renin concentration (r = 0.85, p less than 0.001 erect), plasma renin concentration and plasma angiotensin II concentration (r = 0.86, p less than 0.001 erect), and plasma angiotensin II concentration and plasma aldosterone (r = 0.70, p less than 0.01 erect). In Group 2 there was an inverse correlation between urinary sodium excretion and both urinary aldosterone (r = -0.50) and erect plasma aldosterone (r = -0.36) but, perhaps because of the narrow range of sodium excretion rates, significance was not reached. The normal values in Group 1 indicate that hyperaldosteronism is not essential for the maintenance of established ascites, but do not exclude a role for aldosterone in the control of sodium excretion if it is accepted that renal tubular sensitivity to aldosterone is increased in these patients. In Group 2, the raised mean plasma and urinary aldosterone levels and the trend towards an inverse relationship with urinary sodium excretion suggests a role for aldosterone in the active retention of sodium. It appears that stimulation of the renin-angiotensin system is the major factor in the elevation of plasma aldosterone; there was no relationship between plasma aldosterone and either plasma sodium or potassium levels. The mechanism of renin hypersecretion is unclear but this may represent part of a sympathetically mediated response in order to maintain blood pressure. The close relationship between plasma renin activity and plasma renin concentration indicates that the former is a valid measure of circulating renin levels in cirrhosis, despite low renin-substrate levels.

Lack of effect of oral magnesium on high blood pressure: a double blind study

Seventeen unselected patients with mild to moderate essential hypertension and whose average supine blood pressure after two months' observation with no treatment was 154/100 mm Hg were entered into a double blind randomised crossover study of one month's treatment with magnesium aspartate (15 mmol magnesium/day) and treatment with placebo for a further month. This preparation of magnesium was well tolerated and did not cause diarrhoea. Despite a significant increase in plasma magnesium concentration and a significant increase in urinary excretion of magnesium while taking magnesium aspartate there was no fall in blood pressure compared with either treatment with placebo or values before treatment. The results provide no evidence for a role of dietary magnesium in the regulation of high blood pressure and are contrary to recent speculations.

Renal vein renin studies in renovascular hypertension--do they really help?

Measurement of the renal vein renin ratio (RVRR) is commonly used to predict the response of blood pressure to surgery in hypertensive patients with unilateral renovascular disease. We have reviewed our experience in 37 such patients in whom renal vein renin levels were measured basally and after stimulation of renin secretion with intravenous diazoxide or tilting. Twenty-four patients were cured or improved. When a basal ratio of greater than or equal to 1.5 (diseased: normal kidney) was taken as a positive test the false positive rate was 39% and the false negative rate 71%, there being little difference in outcome between those with ratios above or below 1.5. No other threshold value of RVRR identified those responding to surgery, and acute stimulation of renin secretion did not increase the value of the test. We conclude that the RVRR is of no prognostic value in the surgical treatment of hypertension due to unilateral renovascular disease.

Mononuclear leucocyte intracellular free calcium--does it correlate with blood pressure?

Abnormalities of calcium binding and calcium transport in cells from hypertensive subjects or animals have been previously described. Total cell sodium is reported to be increased in white blood cells from hypertensive subjects; thus by analogy with Blaustein's proposal for the vascular smooth muscle cell, mononuclear leucocyte cytosolic calcium might be increased via a reduction of the Na-Ca exchange. Using the fluorescent calcium indicator, quin 2, cytosolic calcium was measured in mononuclear leucocytes from 22 hypertensive and 19 normotensive subjects. There was no significant difference between the mononuclear leucocyte cytosolic calcium level in the two groups. Incubation of the cells with 10(-4) M ouabain reduced 86 rubidium (86Rb) uptake by 80% of the control value but failed to alter cytosolic calcium. These findings are consistent with a minimal role of the Na-Ca exchange in the mononuclear leucocyte and may explain why the cytosolic calcium was not increased in hypertension despite the previous reports of increased total cell sodium in white blood cells.

Sodium status and the renin-angiotensin-aldosterone system in compensated liver disease

Exchangeable sodium, plasma renin activity, plasma angiotensin II and plasma aldosterone were measured in forty-six control subjects, nineteen patients with chronic non-cirrhotic liver disease and twenty patients with compensated cirrhosis (i.e. without ascites or oedema). In the three groups respectively, mean exchangeable sodium (mmol/kg lean body mass) was 53 (SD = 3), 50 (SD = 5) and 52 (SD = 8). Mean plasma renin activity (pmol l(-1) min(-1)) was 3.2, 3.1 and 3.0 supine and 6.2, 6.2 and 5.1 erect. Mean plasma angiotensin II (pmol l(-1) was 7.3, 5.8 and 6.6 supine and 10.6, 7.9 and 9.0 erect. Mean plasma aldosterone (pmol l(-1)) was 82, 64 and 77 supine and 188, 133 and 121 erect. There were no significant differences among the mean values of any of these variables. These findings indicate that, on the basis of exchangeable sodium measurements, sodium retention is not present in compensated liver disease and that the renin--angiotensin--aldosterone system is essentially normal.