Response of Small Arteries in the Rat Cremaster Muscle to Decreases in Perfusion Pressure

The diameters of the small arteries feeding a microcirculatory bed are determined by the interaction of a number of controlling factors. Neural, humoral, and physical factors all interact to modulate the arterial diameter based on the prevailing local and systemic conditions. The neural and humoral systems are undoubtedly active mechanisms involved in feedback control systems to regulate tissue flow. However, changes in diameter as a result of physical forces, namely, changes in intralumenal pressure, may simply be a local response resulting from changes in vessel wall stresses. There are a number of experimental and pathological conditions in which studies of microvascular diameters are accompanied by significant decreases in systemic pressure. For example, previous studies (1,2) have shown that severe systemic hypoxia in the rat produced a substantial decrease in arterial pressure, and direct measurement of small artery diameters in the rat cremaster muscle showed significant decreases in diameter during the hypoxic forcing (3). Since the decreases in artery diameter are accompanied by decreased systemic pressure, it is logical to assume that at least a portion of the diameter change could be due to simple mechanical relaxation of the vessel wall caused by decreased intralumenal pressure.

To determine the responses of the small arteries in the rat cremaster muscle to decreased intralumenal pressure, we performed graded occlusions of the abdominal aorta to reduce the pressure perfusing the cremaster muscle, while measuring the diameter of the cremasteric microvessels. The results obtained should help to determine the contribution of changes in intralumenal pressure to the changes in diameter of these small vessels during conditions which involve substantial decreases in perfusion pressure such as hemorrhage, systemic hypoxia, anaphylactic shock, or hypotension.

Materials and methods. The results reported in this study were obtained using male, Sprague-Dawley rats anesthetized with sodium pentobarbital (50 mg/kg, ip).