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 phosphate in type II diabetes mellitus (DM) with respect to the absence or presence of renal insufficiency. A euglycemic-hyperinsulinemic clamp was performed in 37 type II DM patients. Subjects were divided into two groups: 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 creatinine levels of 1.5 mg/dL or greater (n =15). Blood and urine samples were collected at the beginning and end of the clamp, and urinary excretion of phosphate was evaluated by calculating fractional excretion (FE-P). Tissue sensitivity to insulin in the whole body was expressed as the glucose infusion rate (M value) and that divided by steady-state plasma insulin levels (M/I ratio) during the last 30 minutes of the 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 the clamp, P <.004), whereas FE-P in group B patients did not change significantly 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 patients 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 percent decrease of FE-P was negatively correlated with blood urea nitrogen ([BUN] r =-.36, P <.05), serum creatinine (r =-.34, P <.05), and serum beta(2)-microglobulin (r =-.44, P <.01) and positively correlated with creatinine clearance (r =.570, P <.004), but it was not correlated 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 related to the glomerular filtration rate but not to systemic insulin insensitivity. The percent decrease of FE-P on clamp study could be useful for assessing the insulin insensitivity of the kidney, which probably occurs primarily in the renal tubules. Copyright (C) 1996 by W.B. Saunders Company.