METHODS

Five adult male volunteers were studied in the fasting state. All were in good health and ranged in age from 25 to 39. Four had normal renal function, and one had proven renal glycosuria. Permission was obtained for the study from each subject by an investigator after a detailed description of the procedures and potential complications. No complications occurred. The study protocol has been approved by the Human Experimentation Committee of the University of Washington affiliated hospitals. Each subject drank 1.0-1.5 liters of water to promote a water diuresis. Each then remained recumbent during the study but stood to void at the end of each urine collection. All infusions were dissolved in normal saline and given in a forearm vein; no glucose was infused. Blood samples were collected from the opposite arm at the midpoint of each period, anticoagulated with heparin, centrifuged immediately, and the plasma separated. The clearance of inulin was used as a measure of glomerular filtration rate (GFR) by a previously described technique(1). Following the inulin priming dose and sustaining infusion, a 45-min equilibration period was allowed, and then three 15-min clearance periods were obtained as controls. After the third control period, an infusion of sterile, pyrogen-free phloridzin (8% phloridzin in 2.5% sodium bicarbonate) was given over a 15-to ZO-min interval in a dose of 100 mg/kg body wt. Four to six study clearance periods each of 15 min were obtained during and following the phloridzin infusion. Osmolalities were measured with an Advanced Instruments osmometer. Uric acid was determined by an enzymatic spectrophotometric method (9). Inorganic phosphate (6), glucose (7), and inulin (12) were measured by methods adapted for a Technicon AutoAnalyzer. The glucose technique is not specific, and other substances such as creatinine, uric acid, and ascorbic acid will give some calorimetric interference. Thus, renal clearances of glucose are only approximate but are indicated as glucose in the text and table.