Regional hemodynamic responses to nicotine in conscious and anesthetized dogs: comparative effects of pentobarbital and chloralose.

This study was conducted in 12 dogs to evaluate regional hemodynamic responses during intravenous infusion of nicotine (36 micrograms/kg/min) in the conscious state and compare them with those in the same dogs following either pentobarbital (n = 6) or chloralose anesthesia (n = 6). Values for regional blood flow were obtained with 15-microns radioactive microspheres and used to calculate regional vascular conductance. In the conscious state, nicotine increased aortic pressure (+70%) and caused hyperventilation that reduced arterial PCO2 (-44%). These systemic effects were associated with decreases in vascular conductance in the renal cortex (-48%), pancreas (-81%), duodenum (-58%), and cerebral cortex (-55%), whereas no significant change in vascular conductance was evident in spleen, liver, or myocardium. Pentobarbital anesthesia blunted the increases in aortic pressure and respiratory activity and the reductions in vascular conductance in the renal cortex, pancreas, duodenum, and cerebral cortex during nicotine infusion. In contrast, chloralose anesthesia accentuated the increase in aortic pressure and the decrease in vascular conductance in the renal cortex during nicotine infusion, while it converted no change in vascular conductance in the spleen into a decrease and no change in vascular conductance in the myocardium into an increase. Chloralose anesthesia blunted nicotine-induced hyperventilation. These findings demonstrate that general anesthetic agents may have markedly different effects on cardiovascular reflex pathways. They emphasize the importance of considering the particular characteristics of the anesthetic agent used in interpreting results from studies of cardiovascular pharmacology and physiology in anesthetized animals.