title: Blood pressure response to phenylephrine infusion in halothane-anesthetized dogs given acetylpromazine maleate.
abstract: To quantitate acetylpromazine-induced alpha-adrenergic receptor blockade, phenylephrine was infused into dogs. The amount of phenylephrine necessary to increase the mean arterial blood pressure (MAP) 50% above base line, with or without the prior administration of acetylpromazine, served to quantify the degree of acetylpromazine-induced alpha-adrenergic receptor blockade. Seven dogs were anesthetized with thiopental, maintained on halothane in oxygen, and mechanically ventilated. All infusions were made through a catheter in the cephalic vein. Continuous recordings were made of MAP and a lead II ECG. After induction of anesthesia, instrumentation, and stabilization of heart rate, MAP, and ventilation, 6 group I dogs were infused with phenylephrine until a 50% increase in MAP was recorded (phenylephrine control). On subsequent research days, each dog was anesthetized, instrumented as described, and given (IV) 1 of 3 dosages of acetylpromazine in the following order--0.05, 0.125, and 0.25 mg/kg. The dose of phenylephrine necessary to increase MAP 50% in the presence of acetylpromazine was recorded. Five group II dogs were studied as in group I, but each dog was given (IM) atropine (0.04 mg/kg) before anesthetization. Two dosages of acetylpromazine were studied in the following order--0.05 and 0.25 mg/kg. Group I dogs, when compared with their phenylephrine controls, were given significantly more phenylephrine to raise MAP 50% at each dose of acetylpromazine studied. The same trend was observed in group II dogs, but at smaller doses of phenylephrine, probably as a result of the positive chronotropic effect of atropine on the heart.
mesh_terms: D000075:Acepromazine / Q000494:pharmacology*; D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D006221:Halothane / Q000494:pharmacology; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects
chemical_list: D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D000075:Acepromazine; D006221:Halothane