VP concentration-response curves in endothelium-intact pressurized MCA segments. Mature multigravid adult (MA, 4?6 months) female (MA F) or age-matched male rats (MA M) and reproductively senescent rats (RS, 10?12 months) female (RS F) or age-matched male rats (RS M). Data points represent means???SE (n?=?6 rats/group). (a-d) 0.0006???P???0.04, mean values without common superscript differ significantly at middle and maximal concentrations of VP.