The effects of a short-time insulin suppression on Na+ excretion were evaluated in 9 type II diabetic hypertensive males. All patients had a body mass index < 26 and normal plasma lipid levels. After 2 weeks under constant NaCl intake (120 mEq of NaCl daily) either octreotide, a somatostatin analogue, or its vehicle were infused in a forearm vein during acute volume expansion (0.20 ml/kg/min isotonic saline given intravenously over a period of 30 min). A double blind randomized cross-over design was followed, and each patient was given both infusions at one week interval. Blood and urine samples for the evaluation of plasma insulin and serum and urine Na+ were taken at time-30, 0, 30, 60, 90, 120, and 240 min. Our data showed that octreotide completely suppressed insulin levels (from time 0 to 60 min). During acute volume expansion+octreotide, Na+ excretion was 0.20 +/- 0.15 mEq/min at time 0, 0.23 +/- 0.21 mEq/min at time 30, 0.64 +/- 0.24 mEq/min at 60 (p < 0.05 vs time 0), 0.71 +/- 0.35 mEq/min at 90 (p < 0.05 vs time 0), 0.78 +/- 0.10 mEq/min at 120 (p < 0.01 vs time 0) and 0.71 +/- 0.12 mEq/min at 240 min (p < 0.05 vs time 0). As compared to acute volume expansion alone, octreotide induced a significant increase of Na+ excretion at 60 and 90 min (p < 0.05). In conclusion, a short-time insulin suppression, as obtained by the somatostatin analogue octreotide, enhances the natriuretic response to intravenous saline load in lean type II diabetic hypertensives.