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.