Measurement of blood flow with radioactive microspheres in the intact and surgically exposed rat cremaster muscle

Abstract

The rat cremaster muscle is used by a number of laboratories as a skeletal muscle model for studies involving in vivo visualization of the microcirculation. However, questions have arisen as to whether the cremaster is a typical skeletal muscle, and as to whether the surgical exposure of the muscle causes any significant alterations in its physiology. To address these questions, we measured total tissue blood flow to the cremaster, biceps brachii, and gastrocnemius muscles of normal, male, Sprague-Dawley rats (weight = 265 ± 53 g, X ± SD ) by the radioactive microsphere method. Polystyrene microspheres, 15 ± 1 μm (nominal diameter), were injected directly into the left ventricle of pentobarbital-anesthesized (50 mg/kg, ip) rats placed on a rodent respirator. Blood to serve as a reference organ was withdrawn at a constant rate of 0.2 ml/min from the cannulated tail artery. Blood flows to each muscle in these animals were (ml/min/100 g): biceps, 10.67 ± 3.22; gastrocnemius, 9.00 ± 1.85; and cremaster, 9.02 ± 2.05, which were not significantly different. Surgical exposure of the cremaster muscle in a controlled tissue bath, identical to that used for our in vivo visualization experiments, did not alter the total blood flow from that observed when the cremaster muscle was intact. Thus, the cremaster muscle appears to be similar to other skeletal muscles with regard to total tissue blood flow and the blood flow does not appear to be altered by surgical exposure under carefully controlled local tissue conditions.