Relationships between blood pressure, age, plasma renin activity and electrolyte excretion in normotensive subjects

Plasma renin activity (PRA), supine and sitting blood pressure (BP) and urinary sodium and potassium excretion were studied in 120 normotensive subjects aged 22--78 years, during strictly standardized conditions. PRA was measured after 1 h supine rest (basal PRA) after ambulation for 3--4 h (upright PRA) and after stimulation with 80 mg frusemide orally (stimulated PRA). PRA was determined with a new, simple, accurate and sensitive radioimmunoassay method. Supine and sitting systolic BP increased with age but no such correlation was found for the diastolic BP. No correlation could be shown between the BP levels and either the sodium or the potassium excretions. PRA levels increased about two-fold from basal to upright levels and about four-fold from basal levels after stimulation. No differences in mean PRA-levels were seen between males and females. We could not demonstrate any correlations between PRA-levels and 24 h sodium or potassium excretions, nor was there any relationship between age and PRA. Reference ranges are given for basal, upright and stimulated PRA in normotensive subjects. From these reference values a rational and clinically useful subdivision into low, normal and high renin groups can be made for hypertensive patients.

Decrease in plasma noradrenaline levels following long-term treatment with prindolol in patients with essential hypertension

15 patients (4 females, 11 males, 21 to 55-year old) with mild to moderate essential hypertension (EH) were treated with placebo for two weeks and thereafter with increasing doses of prindolol (15 to 38 mg/day in the mean) and kept on a mean maintenance dosage of 32 mg/day for an average of 16 weeks in all. Blood pressure (BP), heart rate und plasma noradrenaline (PNA) concentrations were measured under standardized conditions (supine, standing, walking) at the end of two weeks on placebo and after the experimental treatment period. The results were compared to those of a group of 15 normotensive untreated control subjects (NS): after an average of 16 weeks on prindolol BP fell from 163/113 mm Hg to 129/91 mm Hg in the mean. PNA levels in EH before prindolol were significantly higher than in NS (supine: 272 +/- 22.0 ng/l (mean +/- SEM) vs. 135 +/- 15.1 ng/l, standing: 448 +/- 31.9 ng/l vs. 359 +/- 18.4 ng/l, walking: 388 +/- 22.5 ng/l vs. 234 +/- 22.1 ng/l). In EH chronic administration of prindolol led to a significant decrease in PNA concentrations under all the three test conditions to levels which did not differ significantly any more from those derived from NS. The adrenergic response to upright posture reflected in the percentage increase in PNA was significantly less in EH before prindolol when compared to the percentage increase in NS. On prindolol the adrenergic response was not abolidhed, yet it tended to approach the values found in NS. Before prindolol under resting conditions diastolic BP correlated closely with the corresponding PNA levels (p less than 0.01, r = 0.66, n = 15). This correlation could not be reestablished after prindolol treatment. The decrease in PNA after long-term treatment with prindolol was not correlated to the fall in blood pressure. The decrease in PNA indicates a lower activity of the sympathetic nervous system which may contribute to the antihypertensive effect of prindolol.

Measurement of renin concenration in human plasma using 125i-labelled sheep renin substrate

Sheep renin substrate was prepared 28% pure, labelled with 125I and then diluted in concentrated unlabelled sheep substrate. Ten percent of the 125I-label was released as a small fragment on incubation with excess human renin. Adequate separation of the labelled fragment from the parent protein was accomplished with charcoal precipitation or gel filtration. Renin concentration in human plasma was assayed by incubating the 125I-labelled substrate with plasma under zero-order kinetic conditions. Renin was assayed in plasma that had been either acidified or untreated. The acidification procedure was employed to activate inactive renin which accounted for more than half of the total plasma renin concentration. The results of this radiochemical assay correlated closely with the results of bioassay. Specificity of the method was established with antirenin. The assay was sufficiently sensitive to measure suppressed plasma renin levels. The iodinated substrate was stable on storage at -10 degrees C over a six-month period. Because of its high affinity for human renin, ease of purification and stability of the iodinated product, sheep substrate provides a convenient means for routine determination of plasma renin concentration by radiochemical assay.