Anesthetic depression of microcirculation, central hemodynamics, and respiration in decerebrate rats

The objectives of this study were the development of a skeletal muscle microcirculatory preparation, in which the complications of drug anesthesia were minimized, and the quantitation of the effects of urethan and chloralose anesthesia on the microcirculation. Rats were initially anesthetized with urethan and chloralose and decerebrated by a midcollicular transection. The cremaster skeletal muscle, with intact circulation and innervation, was prepared for intravital microscopy by placement in a tissue bath. Arterioles (9-70 micrometers diam) at several anatomic levels were observed during the initial period of urethan-chloralose anesthesia (period 1), after recovery from the anesthesia (period 2), and again following reanesthetization (period 3). During period 2, respiratory rate, heart rate, and mean arterial pressure were significantly greater than during periods 1 and 3. Smaller arterioles (8-50 micrometers diam) exhibited vasomotion (mean amplitude 35% of mean diameter; mean frequency 31 cycles/min) during period 2. Urethan-chloralose anesthesia during periods 1 and 3 inhibited vasomotion and increased arteriolar diameters by 16-36%. This study quantitates the depressant effects of urethan-chloralose anesthesia on the cardiovascular system and demonstrates the feasibility of using decerebration to circumvent the necessity of continuous drug anesthesia for in vivo microvascular studies.