EFFECT OF INSULIN ON URINARY PHOSPHATE EXCRETION IN TYPE-II DIABETES-MELLITUS WITH OR WITHOUT RENAL-INSUFFICIENCY

We investigated the effect of insulin on urinary excretion of phosphat e in type II diabetes mellitus (DM) with respect to the absence or pre sence of renal insufficiency. A euglycemic-hyperinsulinemic clamp was performed in 37 type II DM patients. Subjects were divided into two gr oups: group A consisted of patients with serum creatinine levels less than 1.5 mg/dL (n =22), and group B consisted of patients with serum c reatinine levels of 1.5 mg/dL or greater (n =15). Blood and urine samp les were collected at the beginning and end of the clamp, and urinary excretion of phosphate was evaluated by calculating fractional excreti on (FE-P). Tissue sensitivity to insulin in the whole body was express ed as the glucose infusion rate (M value) and that divided by steady-s tate plasma insulin levels (M/I ratio) during the last 30 minutes of t he clamp. FE-P in group A patients significantly decreased during the clamp (from 9.46 +/- 0.67% before the clamp to 7.12 +/- 0.73% after th e clamp, P <.004), whereas FE-P in group B patients did not change sig nificantly during the clamp. The percent decrease of FE-P (decrease of FE-P during the clamp divided by FE-P before the clamp) in group A pa tients was significantly higher than in group B patients (22.5 +/- 7.0 % and 2.5 +/- 5.1%, respectively, P <.04). In all 37 patients, the per cent decrease of FE-P was negatively correlated with blood urea nitrog en ([BUN] r =-.36, P <.05), serum creatinine (r =-.34, P <.05), and se rum beta(2)-microglobulin (r =-.44, P <.01) and positively correlated with creatinine clearance (r =.570, P <.004), but it was not correlate d with the M value or M/I ratio. These results showed that the kidneys of diabetic patients with renal insufficiency are insulin insensitive in terms of phosphate transport, and the insulin insensitivity is rel ated to the glomerular filtration rate but not to systemic insulin ins ensitivity. The percent decrease of FE-P on clamp study could be usefu l for assessing the insulin insensitivity of the kidney, which probabl y occurs primarily in the renal tubules. Copyright (C) 1996 by W.B. Sa unders Company.