Acute effects of wortmannin on insulin's haemodynamic and metabolic actions in vivo

Wortmannin, an inhibitor of phosphatidylinositol 3-kinase, was systemically infused during a hyperinsulinemic euglycemic clamp to investigate its effects in vivo. Rats were infused under anesthesia with saline, 10 or 20 mU·min–1·kg–1 insulin, wortmannin (1 µg·min–1·kg–1) + saline, or wortmannin + insulin (10 mU·min–1·kg–1); wortmannin was present for 1 h before and throughout the 2-h clamp. Femoral blood flow (FBF), glucose infusion rate to maintain euglycemia (GIR), glucose appearance (Ra), glucose disappearance (Rd), capillary recruitment by 1-methylxanthine metabolism (MXD), hindleg glucose uptake (HLGU), liver, muscle, and aorta Akt phosphorylation (P-Akt/Akt), and plasma insulin concentrations were determined. Plasma insulin increased from 410 ± 49 to 1,680 ± 430 and 5,060 ± 230 pM with 10 and 20 mU·min–1·kg–1 insulin, respectively. Insulin (10 and 20 mU·min–1·kg–1) increased FBF, MXD, GIR, Rd, and HLGU as well as liver, muscle, and aorta P-Akt/Akt and decreased Ra (all P < 0.05). Wortmannin alone increased plasma insulin to 5,450 ± 770 pM and increased Ra, Rd, HLGU, and muscle P-Akt/Akt without effect on blood glucose, FBF, MXD liver, or aorta P-Akt/Akt. Wortmannin blocked FBF, MXD, and liver P-Akt/Akt increases from 10 mU·min–1·kg–1 insulin. Comparison of wortmannin + 10 mU·min–1·kg–1 insulin and 20 mU·min–1·kg–1 insulin alone (both at 5,000 pM PI) showed that wortmannin fully blocked the changes in FBF and Ra and partly those of GIR, Ra, Rd, HLGU, and muscle P-AKT/Akt. In summary, wortmannin in vivo increases plasma insulin and fully inhibits insulin-mediated effects in liver and aorta and partially those of muscle, where the latter may result from inhibition of insulin-mediated increases in blood flow and capillary recruitment