Influence of pentobarbital and morphine-chloralose anesthesia on the autonomic cardiovascular function and on drug responses in mongrel dogs

The major objectives of this investigation were to evaluate certain autonomic and cardiovascular effects of morphine-chloralose and pentobarbital anesthesia in mongrel dogs and to determine the influence of the two anesthetics on the effect of certain pharmacological agents. Alterations in the hindleg vascular reactivity and cardiovascular reflexes produced by pentobarbital (P) 35 mg/kg, i.v., and morphine (M) 3 mg/kg, i.m., plus chloralose (C) 100 mg/kg, i.v., were evaluated in mongrel dogs. Comparison of pressure-flow curves indicated that there was a significant reduction in the hind limb vascular resistance in dogs anesthetized with P. However, acute denervation plus the administration of an alpha-blocker produced identical shifts of the pressure-flow curves to the right in both groups, suggesting that the neurogenic tone and tone contributed by circulating catecholamines were of equal magnitude in the dogs under the influence of P or M + C. Thus, the major difference appears to be that the intrinsic vascular tone of the smooth muscle was significantly depressed by P anesthesia. Reflex increase and decrease in perfusion pressure in response to bilateral carotid occlusion and i.v. norepinephrine respectively, were significantly greater in M + C dogs. Reflex bradycardic responses to i.v. phenylephrine and norepinephrine were also significantly greater in M + C animals compared to those anesthetized with P. Further, blood pressure and heart rate responses to carotid sinus nerve stimulation were more pronounced in the M + C animals. These results indicate that while the resting neurogenic tone to the hind limb vasculature is identical in M + C or P anesthetized dogs, cardiovascular reflexes are more responsive in M + C anesthetized animals. [...]