Effect of pH change upon systemic large and small vessel resistance.

In the dog foreleg acute increase and decrease of hydrogen ion concentration is associated with active small vessel dilatation and constriction, respectively, through some direct effect upon vascular smooth muscle. These small vessel resistance changes do not affect total resistance in the intact leg because of directionally opposite active changes in artery resistance. The latter response appears to be related tn central nervous connections and perhaps to circulating or locally released epinephrine, norepineohrine or unknown vasoactive substances.