Arteriolar and venular reactivity to superfusate pO2 in tissues with different metabolic capacity. A study in skeletal muscle and mesentery of the rat.

In skeletal muscle (extensor hallucis proprius) and mesentery of anesthetised (pentobarbital 30 mg/kg) female rats (200 g) we have compared reactivity to O2 of arterioles and venules with their response to a vasoconstrictor (epinephrine 5.5 x 10(-7) M) and a vasodilator (adenosine 10(-4) M). Muscle arterioles fully constricted with O2 and epinephrine and dilated with adenosine (22%). Muscle venules did not respond to changes in superfusate pO2, constricted 18% with epinephrine and dilated 10% with adenosine. In the mesentery changes in superfusate pO2 had no effect on diameters of arterioles or venules but epinephrine fully constricted arterioles and constricted venules by 19%, while adenosine dilated arterioles (6%) but not venules. When we set arteriolar and venular diameters during adenosine superfusion at 100%, muscle arterioles appeared to operate at 63% and mesenterial arterioles at 84% of maximal diameter at normal tissue pO2. For venules these percentages were 91 and 97%, respectively. Arterioles and venules in muscle thus have higher tone and muscle arterioles are greatly sensitive to changes in tissue pO2 while in our preparation mesenterial arterioles are not.