VP concentration-response curves in MCA segments in the absence or presence of selective COX inhibitors. Preparations were studied in triplicate from each animal group: mature multigravid adult (MA, 4?6 months) female (MA F) (A) or age-matched male rats (MA M) (B), reproductively senescent (RS, 10?12 months) female (RS F) (C), or age-matched male rats (RS M) (D). Data points represent means???SE (n?=?6 rats/group). (a-f) 0.0001???P???0.02, mean values without common superscript differ significantly at middle and maximal concentrations of VP. In RS M, there were no significant differences among CTL, SC560, and NS398 groups.