The objective of this research proposal is to determine whether there is a relationship between intrarenal blood flow distribution and electrolyte excretion. In the course of this study, the effects of selected natriuretic and antinatriuretic agents on intrarenal blood flow distribution will be determined and compared with the fractional excretion of sodium and potassium. Blood flow distribution between outer and inner cortices will be measured with labelled microspheres before (Yb169) and after (Sr85) natriuresis or antinatriuresis. In addition to studying the effects of various pharmacological agents such as furosemide and ethacrynic acid on blood flow distribution and electrolyte excretion, studies with aldosterone and antidiuretic hormone are planned. Finally, experiments are proposed to test the possibility that renal sympathetic nerves play a role in regulating electrolyte excretion through redistribution of renal blood flow. These studies will include stimulation of renal sympathetics, acute renal denervation and/or administration of adrenergic blocking agents.