RESUMO
A denervated, isolated canine hindlimb (HL) model was developed to minimize residual anesthetic contamination. To test the preparation, we determined the peripheral arterial vascular effects of atropine sulfate and the effect of the basal anesthetic on arterial resistance. In four dogs that were under halothane and oxygen anesthesia, the HL was prepared to allow either vascular isolation of the limb or continuity with the systemic circulation. During isolation the HL was perfused by roller pump at a preset flow rate through an infant oxygenator. Inspired gas fed to the oxygenator contained either 0%, 1.25%, or 2.5% halothane to determine that anesthetic's effect on HL arterial vascular resistance. No halothane (0%) was used in the oxygenator inflow during the atropine measurements. Vascular resistance was calculated from HL arterial pressure at constant flow. Halothane caused a significant stepwise fall in vascular resistance, with a decrease of 68% at 2.5% inspired concentration (p less than 0.01). Atropine produced a progressive attenuation of resistance that decreased by 18% after the 2.5 mg/kg dose (p less than 0.01). The model proved stable over time and demonstrated an apparent direct, dose-dependent vasodilating effect of both atropine and halothane in the canine HL muscle arterial bed.
Assuntos
Atropina/farmacologia , Halotano/farmacologia , Membro Posterior/irrigação sanguínea , Resistência Vascular/efeitos dos fármacos , Animais , Circulação Sanguínea/efeitos dos fármacos , Cromatografia Gasosa , Denervação , Modelos Animais de Doenças , Cães , Halotano/sangue , Membro Posterior/efeitos dos fármacosRESUMO
Under halothane anesthesia five dogs were prepared with both hindlimbs isolated from the systemic circulation to allow intermittent placement on extracorporeal perfusion at constant flow. One limb of each dog was surgically denervated. In this relatively anesthetic-free preparation, graded equivalent doses of alfentanil, fentanyl, and sufentanil were infused over 30 s, and vascular resistance was measured. Increasing opioid administration caused a progressive diminution in peripheral resistance. By the high dose level, alfentanil (500 micrograms/kg), fentanyl (50 micrograms/kg), and sufentanil (6 micrograms/kg) caused equal and significant decreases of 48%, 48%, and 44% in resistance, respectively. There was no difference among the opioids in effects on resistance at equivalent dosages. Neither pretreatment with naloxone nor denervation changed the response to the narcotics. We conclude that the three synthetic opioids produce vasodilation by direct action on the peripheral vascular smooth muscle.