The purpose of this study was to examine the effects of ketamine and pentobarbital on venous capacitance in rats. Venous capacitance was assessed by measuring the mean circulatory filling pressure (MCFP) at three levels of blood volume in conscious rats as well during anesthesia with ketamine (125 mg/kg, ip) or pentobarbital (50 mg/kg, ip). MCFP was measured during brief periods of circulatory arrest produced by inflating an indwelling balloon in the right atrium. MCFP was maintained during ketamine anesthesia at a level similar to that measured in conscious animals, while it was decreased (P < 0.01) during pentobarbital anesthesia both at normal blood volume and following hemorrhage. These results suggest that ketamine did not alter but pentobarbital increased venous capacitance. The slope of the regression line relating MCFP and blood volume was not altered by ketamine but was increased (P < 0.05) by pentobarbital, which suggests that ketamine did not alter but pentobarbital decreased total vascular compliance. These results suggest that ketamine maintains but pentobarbital decreases venous tone.
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