LEP and obesity due to melanocortin 4 receptor deficiency: Rat portal veins were treated with leptin at a concentration of 3.1 nmol/L (50 ng/mL) due to its equivalence to leptin concentrations in obesity (Maffei et al., 1995; Rajapurohitam et al., 2003; Zeidan et al., 2005) for 24 h and the ratio of F/G-actin was calculated and normalized to unstretched (untreated) RPVs (Figure 3D).