AIM: To investigate the effects of milrinone (a selective phosphdiesterase III inhibitor PDE 3) on insulin secretion, blood glucose, plasma free fatty acids (FFA) and dose-response relationship, and assess possible effects of milrinone on glucose metabolism and insulin sensitivity in conscious rats. METHODS: The catheterized nonstressed rats were administered by the varying doses of milrinone (1, 5, 25 ?mol/kg) and were compared with controls. A hyperinsulinaemic- euglycaemic clamp was established in awake rats, and milrinone(25 ?mol/kg) and 25% dimethyl sulfoxide (DMSO, as a control) were given at 120 min during hyperinsulinaemic- euglycaemic clamp. Glucose turnover was decided by gas chromatograph mass spectrometer (GC-MS). RESULTS: After dosing, plasma FFA levels in 3 milrinone groups significantly increased compared with the controls and before dosing. The percentages of elevation of FFA by the different milrinone doses were very similar, 50%, 52%, 55% for 1, 5, 25 ?mol/kg respectively at 2 min after dosing. Plasma insulin levels were significantly elevated in the 5 and 25 ?mol/kg groups, and the effect of milrinone on glucose concentration was detectable only 25 ?mol/kg group. During hyperinsulinaemic clamp, there were significant increase in plasma FFA (from 173.1?15 2 to 633 8?87 3 ?Eq/L) and hepatic glucose production (HGP), and a significant decrease in glucose infusion rates (GIR) (to about 21%). CONCLUSION: These data suggest that milrinone impaires the abilities of insulin to suppress lipolysis and HGP, and insulin-mediated glucose utilization in peripheral tissue. Therefore, milrinone administration may induce an acute insulin resistance in vivo.