Differential effects of general anesthetics on regional vasoconstrictor responses in the rat

Although many cardiovascular experiments are performed in the presence of anesthetics, little is known about the depressant effect on regional vascular reactivity. The effect of 2 commonly used anesthetics, pentobarbital (PB) and a chloralose urethane mixture (C-U) on vascular reactivity of different tissues was studied in rats. In order to measure blood flow, rats were equipped with miniaturized Doppler flow probes on the renal artery, the superior mesenteric artery and abdominal aorta. Catheters were implanted for measuring blood pressure and for i.v. injections of differently acting vasopressor substances. Vasoconstriction was induced by i.v. noradrenaline (NA), phenylephrine (P) and angiotensin II (AII), in conscious animals and in anesthetized rats (PB or C-U). The 3 vasopressor substances caused a dose-dependent increase in regional vascular resistances. In anesthetized animals, constrictor responses following P were not affected in any beds. PB diminished the effect of NA and AII in all vascular beds studied, while C-U only depressed renal and splanchnic reactivity. During C-U anesthesia, hindquarter vascular reactivity was not affected. This indicates that anesthetics exert differential regional effects, depending upon the substances studied. This complicates extrapolation of experimental data from one bed to other vascular beds or to conscious animals.