Figure 3. Increased EC50 of constriction to NA but not dilatation to ACh .
A, concentration‐dependent constriction to NA is shifted to the right in Old MAs compared to Young MAs. Initial resting IDs were 199 ± 12 for Young MAs and 187 ± 10 μm for Old MAs; respective IDs were 76 ± 7 and 80 ± 6 μm during peak constriction to NA and were 217 ± 12 and 206 ± 11 μm during maximal dilatation. B, concentration‐dependent dilatation to ACh is similar in Old and Young MAs. Initial baseline IDs during preconstriction with NA (1 μm) were not different between age groups (Young, 107 ± 7 μm; Old, 101 ± 9 μm). Peak IDs during vasodilatation to ACh were 174 ± 2 and 166 ± 12 μm, respectively; corresponding maximal IDs were 211 ± 3 μm and 201 ± 12 μm. % Constriction and % Max dilatation calculated as described in Methods. n = 5 MAs per age group. *P < 0.05, Young versus Old MAs at same NA concentration.