This is termed the metabolic theory of blood flow regulation. Increases or decreases in metabolism will increase or decrease the release of these vasodilator substances. Another mechanism that may couple blood flow and metabolism involves changes in the partial pressure of oxygen. Note, however, that hypoxia induces vasoconstriction in the pulmonary circulation. Adenosine formation increases during hypoxia and increased oxygen consumption, especially if the latter is accompanied by inadequate oxygen delivery.
Adenosine formation is a particularly important mechanism for regulating coronary blood flow.
Potassium ion is released by contracting cardiac and skeletal muscle. Potassium ion appears to play a significant role in causing active hyperemia in contracting skeletal muscle. Carbon dioxide formation increases during states of increased oxidative metabolism. It readily diffuses from parenchymal cells where it is produced to the vascular smooth muscle of blood vessels where it causes vasodilation. CO 2 plays a significant role in regulating cerebral blood flow.