We propose to study renal tubular transport of glucose in the dog by micropuncture techniques with an emphasis on its relationship to phosphate and sodium transport. Recollection micropuncture experiments of the proximal and distal tubule will be carried out before and after various maneuvers to alter glucose, phosphate or sodium transport, with or without glucose loading to saturate the tubular transport capacity for glucose. Glucose in the tubule fluid will be analyzed by ultramicrofluorometric method with hexokinase, phosphate by colorimetric method using ascorbic acid, and sodium by spectrophotometry using helium glow photometer. The following experiments will be carried out. The effect of glomerular filtration rate (GFR) on glucose transport will be examined by altering GFR with aortic constriction. The effect of extracellular volume expansion on glucose reabsorption will be compared with that on phosphate and sodium transport. The effect of parathyroid hormone on glucose transport will be compared with its inhibitory effect on phosphate reabsorption. The effect of phlorhizin, which blocks glucose reabsorption, will be studied in relation to phosphate transport. Finally, the agents such as acetazolamide and maleic acid will be administered to inhibit proximal tubule sodium reabsorption and their effect on glucose and phosphate transport will be studied. These experiments are designed to examine whether: 1) maximum tubular reabsorptive capacity for glucose is GFR dependent; 2) proximal tubule glucose transport is in part sodium dependent; 3) proximal tubule glucose and phosphate transports share the common pathway or are inversely related; and 4) any glucose reabsorption occurs in the distal nephron as compared to that of sodium and phosphate. The information obtained from the present project will provide better insight into renal handling of glucose and thereby facilitate the diagnosis and management of the clinical conditions in which renal glucose transport is altered.