Compensatory vasoconstrictor effects of sodium pentobarbital on the hindquarters of conscious normotensive control and lumbar-sympathectomized Wistar rats

The aim of this study was to compare the vasoconstrictor effect of sodium pentobarbital on the hindquarter resistance of intact control Wistar rats with the effect on lumbar-sympathectomized rats. For this purpose, mean arterial pressure (MAP) and hindquarter (supplied terminal aorta) flow (HQF) were simultaneously measured in these conscious rats with an arterial in dwelling cannula and electromagnetic flow probe implanted around the terminal aorta. Hindquarter resistance (HQR) was calculated as MAP divided by HQF. In the intact control conscious rats, subsequent pentobarbital anesthesia (30 mg/kg, i.v.) caused an increase in HQR (+43.5±7.4%, mean±S.E.M.) and a decrease in MAP (−17.0±3.2%). After pentobarbital anesthesia, subsequent ganglionic blockade with hexamethonium bromide (C6; 25 mg, i.v.) induced a significant decrease in HQR (−30.9±3.0%) with a further lowering of MAP (−20.9±1.6%). However, in rats not anesthetized with sodium pentobarbital, C6 alone induced almost no change in HQR (−3.4±5.3%), even when MAP was lowered (−24.2±2.5%). In the lumbar-sympathectomized rats, pentobarbital anesthesia produced almost no change in HQR (−11.7±4.4%), although MAP decreased significantly (−24.3±2.2%). These findings suggest that: (1) sodium pentobarbital anesthesia newly generates a compensatory vasoconstrictor tone in the hindquarters acting against the depressor effect, and (2) the vasocompensator tone is controlled by the efferent fibers, including those in the lumbar sympathetic nerves.