Renal micropuncture techniques and microperfusion of nephron segments in vivo will be used to measure pressures, flows, permeabilities and protein concentration for the proposed work. Studies will include examining the relationship between glomerulo-tubular balance and tubulo-glomerular feedback. Mechanisms of glomerulo-tubular balance will be evaluated and the role of intraluminal and extraluminal factors will be quantitated. Radioimmunoassay techniques will be utilized to determine changes in antidiuretic hormone levels in plasma in both normal and chronic sodium depleted rats. The study examining Angiotensin II (AII) receptors in the proximal convoluted tubule will examine the influence of both media and temperature on AII receptors in the proximal convoluted tubule.