Comparison of arteries with longitudinal and circular venous muscle from the rat.

Rat portal, mesenteric, renal, and femoral veins possess functionally responsive circular and longitudinal smooth muscle layers in vitro. In contrast to the dominant rhythmically active longitudinal muscle of portal veins, rat longitudinal mesenteric veins lacked rhythmic activity and developed maximal force equivalent to that of mesenteric circular muscle. Renal and femoral veins exhibited predominantly circular smooth muscle responses. Rat veins must be subjected to between 1 g (renal and femoral) and 4 g (circular portal and mesenteric) of passive forse for optimal responsiveness. Contractile response to vasoactive agent including carbamylcholine, serotonin, and norepinephrine was quantitatively different among veins. Femoral veins developed greater maximal force in response to norepinephrine than to KCL, and the responses to norepinephrine were not altered by cocaine. In contrast, cocaine markedly potentiated responses to norepinephrine in portal, mesenteric, and renal veins and, to a lesser extent, in the mesenteric artery. These data demonstrate heterogeneity in rat venous tissue and suggest that neuronal innervation may markedly influence responses to norepinephrine in some, but not all, rat blood vessels.