This project was supported by the Oregon Health and Science University Knight Cardiovascular Institute, Center for Developmental Health and the Struble Foundation. There are no competing interests.

In the intact rat, short loops of Henle, distal and proximal tubules were studied by microperfusion. The same loop of Henle was perfused at 4 or more perfusion rates and net and fractional absorption of sodium was determined. When the perfusion rate increased a greater net amount of sodium was absorbed but the fractional absorption of sodium decreased from 80% at 10 nl/min to 50% at 40 nl/min. The fractional absorption of water fell from 65% to 30% with the same change in perfusion rates. In the distal tubule more sodium was absorbed and more potassium was secreted when the perfusion rate was increased. Saline infusion depressed sodium absorption by the proximal tubule but in the loop of Henle and distal tubule there was no depression of sodium absorption. The rate and amount of potassium entering across the distal tubule epithelium was not affected by the saline infusion. The natriuresis after saline infusion is produced in part by depression of sodium absorption in the proximal tubule. It has been postulated that in addition saline expansion acts at a distal site. If the results found in the short loops of Henle are representative of the rest of the kidney then sodium transport in either the collecting tubule or the collecting duct must be inhibited.

SummaryBeta adrenergic blocking drugs were found to be effective hypotensive agents in the long-term treatment of patients with hypertension. In 40 % of patients they appeared to be an extremely satisfactory antihypertensive agent. The fall in blood pressure was confirmed in a double blind study which also indicated that propranolol, prindolol, alprenolol and MK 950 (timolol) had similar antihypertensive properties. Propranolol and timolol reduced the pulse rate more than prindolol and alprenolol but the fall in blood pressure induced by the four drugs was not significantly different.

1 Propranolol and pindolol reduced both the blood pressure and plasma renin activity when given chronically to hypertensive patients. 2 There was no correlation between the fall in blood pressure and the fall in plasma renin activity. 3 Neither the basal nor the random plasma renin activity predicted the patients who would respond to beta‐adrenergic receptor blocking drugs. 4 Oral propranolol reduced plasma renin activity but did not reduce blood pressure within 4 h of administration; oral pindolol reduced blood pressure but did not reduce plasma renin activity within 4 h of administration. 5 The reduction of blood pressure by propranolol and pindolol does not seem to be mediated by changes in plasma renin in most patients.

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1 The control of blood pressure achieved was similar whether pindolol or propranolol was given once or three times daily. 2 When the drugs were ceased the antihypertensive effect lasted for longer than 24 h. There was no rebound hypertension. 3 The full effect of the drug on blood pressure was seen within 24 h of its recommencement. 4 Changes in blood pressure, pulse rate, and plasma renin activity occurred but these were not considered to be causally related.

No abstract

1. As part of a study investigating the effect of dietary alterations of sodium and potassium intake on blood pressure, the changes in nutrients that occurred with dietary intervention were determined. 2. Mild hypertensive subjects were randomized to one of four dietary intervention groups: control; high potassium; low sodium; low sodium, high potassium. The changes in nutrients in each diet group were assessed by dietary history and five repeat 24 h dietary recalls. Assessment was validated by measurement of urinary nitrogen excretion and urinary electrolytes. 3. The three dietary intervention groups experienced a fall in blood pressure (systolic: 4.4 +/- 1.0 mmHg, P less than 0.005; diastolic: 3.3 +/- 0.7 mmHg, P less than 0.001), greater than that observed in the control group. 4. The only significant dietary change across all diet groups was a reduction in the dietary sodium/potassium ratio, which was significantly less than that of the control group. The only other nutrient to differ from the control in all groups was fat intake, which was reduced. 5. In the control group there was a small but significant decrease in energy, fibre, protein, carbohydrate, potassium and magnesium intake. In the high potassium group there was a significant increase in fibre, carbohydrate, potassium, magnesium, and a decrease in calcium intake. In the low sodium group there was a decrease in energy intake with a subsequent reduction in all nutrients except alcohol. In the low sodium, high potassium group there was a significant reduction in dietary sodium and protein and an increase in fibre, carbohydrate, potassium and magnesium. 6. The reduction of the dietary sodium/potassium ratio correlated with a reduction in the urinary sodium/potassium ratio. This was the best predictor for change in diastolic pressure in all groups, suggesting that reduction in the sodium/potassium ratio contributed to the fall in blood pressure. 7. Reduction of sodium intake and increase in potassium intake by dietary means caused a reduction in blood pressure which does not appear to be due to alteration of other measured dietary constituents.