Figure 16.

The vasodilator response to a single forearm contraction at 20% of maximum is reduced by ∼80% when nitric oxide, prostaglandin, and K⁺-mediated hyperpolarization vasodilator pathways are inhibited. Blockade of NO and PGs alone can reduce this response ∼50%, and blockade of K⁺-mediated hyperpolarization alone can reduce it by ∼60%. At this time, it is not known if blockade of all of these pathways in combination will affect the steady-state blood flow responses to exercise. This is perhaps the most complete blunting of a vasodilator response to contractions currently available and highlights the idea that the vasodilator responses to contractions are highly redundant. It is also interesting to note that the immediate vasodilator responses to contractions can be blunted in conditions like aging (76, 85, 253). (Figure provided by Drs. Anne Crecelius and Frank Dinenno.)