Blood Flow Regulation by Adenosine in Heart, Brain, and Skeletal Muscle

Although it has long been recognized that adenosine is a potent vasodilator, only during the past 20 years has serious consideration been given to its possible role in the local regulation of blood flow. Prior to that time other potential mediators of regional blood flow regulation, such as reduced PO2, increased PCO2, or decreased pH were often suggested, but definitive experimental proof for a physiological role for these agents was lacking. In more recent years, more evidence has appeared in support of a reduced pH, and additional substances such as potassium ions, inorganic phosphate, and increased osmolarity have been suggested with varying degrees of acceptance. In all likelihood, several factors, including a myogenic response, are involved in local blood flow regulation, but adenosine appears to be the primary factor. Since most of the studies on adenosine have been focused on its mediation of the control of coronary, cerebral, and skeletal muscle blood flow, in that order, discussion will be limited to these three tissues. This in no way means that adenosine does not act similarly in several other tissues. In the kidney, however, adenosine induces vasoconstriction, a subject considered in detail by Dr. Osswald in Chapter 25.