1. To obtain information about the mechanism of the natriuresis induced by angiotensin, its effect on the distribution of electrolytes, urea and water in rabbit kidneys was examined.
2. In five control experiments, after infusion of normal saline at a low rate for several hours, the animals were killed and their kidneys removed and analysed for Na, K, Cl, urea and water content at five levels from outer cortex to papilla. In five further animals, the infusion was changed to 1 μg kg−1 min−1 of angiotensin for 40 min. This induced a significant natriuresis.
3. Significant changes in tissue composition induced by angiotensin were reduction in the Na, Cl, and urea concentrations throughout the medulla and papilla, an increase in the water content in these regions and an increase in outer cortical Na and Cl concentrations. In the inner cortex the water content was increased and the urea content decreased.
4. Angiotensin produced similar changes in renal tissue in experiments in which the same protocol was used in eight adrenalectomized rabbits and in five rabbits with unilateral renal denervation. The changes seen were therefore ascribed directly to angiotensin and not to adrenal hormone release or sympathetic nerve stimulation.
5. The most likely interpretation of the results is that angiotensin inhibits Na reabsorption in the ascending limb of the loop of Henle. However, other explanations, including alterations in vasa recta blood flow, are possible.