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

The aim of this study was to compare the vasoconstrictor effect of sodium p entobarbital on the hindquarter resistance of intact control Wistar rats wi th the effect on lumbar-sympathectomized rats. For this purpose, mean arter ial pressure (MAP) and hindquarter (supplied terminal aorta) flow (HQF) wer e simultaneously measured in these conscious rats with an arterial in dwell ing cannula and electromagnetic Row probe implanted around the terminal aor ta. Hindquarter resistance (HQR) was calculated as MAP divided by HQF. In t he intact control conscious rats, subsequent pentobarbital anesthesia (30 m g/kg, i.v.) caused an increase in HQR (+43.5+/-7.4%, mean+/-S.E.M.) and a d ecrease in MAP (-17.0+/-3.2%). After pentobarbital anesthesia, subsequent g anglionic blockade with hexamethonium bromide (C6; 25 mg, i.v.) induced a s ignificant 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 l owered (-24.2+/-2.5%). In the lumbar-sympathectomized rats, pentobarbital a nesthesia produced almost no change in HQR (-11.7+/-4.4%), although MAP dec reased significantly (-24.3+/-2.2%). These findings suggest that: (1) sodiu m pentobarbital anesthesia newly generates a compensatory vasoconstrictor t one in the hindquarters acting against the depressor effect, and (2) the va socompensator tone is controlled by the efferent fibers, including those in the lumbar sympathetic nerves. (C) 2000 Published by Elsevier Science B.V. All rights reserved.