Effect of pentobarbital anesthesia on the pressor response to agonists in vivo in normal and endotoxemic rats.

Studies of cardiovascular physiology are frequently performed under barbiturate anesthesia even though the effect of barbiturates on the pressor response to catecholamines is controversial, and their effect on the response to other agonists is unknown. The effect of pentobarbital (PB) anesthesia on the pressor and heart rate (HR) dose responses to norepinephrine (NE), angiotensin II (AII), vasopressin (VP) and neuropeptide Y (NPY) was studied in vivo in normal and endotoxemic rats. Four groups of rats (5-6 rats/group) were studied for each agonist: 1) anesthetized/endotoxemic, 2) anesthetized/control, 3) conscious/endotoxemic, and 4) conscious/control. Anesthesia was maintained with 10 mg/kg of PB i.v. q 45 minutes. Endotoxemia was established by infusion of a non-hypotensive dose of E. coli lipopolysaccharide 0127:B8, (LPS, 10 micrograms/10 microliters/min) throughout the experiment. One hour after the LPS (or saline control) infusion was started, dose response curves of the pressor and HR responses to agonists were established. LPS infusion resulted in marked suppression of the pressor response to NE, AII, and VP in both conscious and anesthetized rats. LPS infusion suppressed the response to NPY in conscious, but not in anesthetized rats. LPS did not affect the baroreceptor reflex. In both normal and endotoxemic rats, PB anesthesia suppressed the pressor response and attenuated the baroreceptor reflex to AII and NPY, enhanced the pressor response without affecting the heart rate response to NE, and attenuated the baroreceptor reflex to VP. The pressor response to VP was suppressed by anesthesia in normal, but not in endotoxemic rats. PB anesthesia interferes with the cardiovascular effects of different agonists in a variable manner, depending on the agonist tested and the presence or absence of endotoxemia, indicating their different modes of action. These effects should be considered when planning in vivo experiments with these and other agonists.