Abstract
Summary
Acetylcholine, histamine, norepinephrine, epinephrine and serotonin were injected intravenously in varying doses into 20 adult mongrel dogs. Phenoxybenzamine (Phb.) was then administered by intravenous infusion to 15 dogs. One hour after the infusion, the drugs were again administered in the same dosages. Portal vein and systemic artery pressure responses to all drugs were monitored and degree of Phb. blockade was evaluated for each drug used. Results indicate that the greatest number of significantly blocked responses are seen with 5 mg/kg of Phb. for acetylcholine and histamine; with 10 mg/kg Phb. for serotonin, and 5 and 10 mg/kg; Phb. for epinephrine and norepinephrine. The portal venous responses to acetylcholine, histamine and serotonin have a greater number of significant differences than the arterial responses. However, all the drugs tested were partially blocked by phenoxybenzamine. The results of these experiments emphasize the lack of specificity exhibited by this adrenergic blocking agent. The action of Phb. in blocking the portal vein pressure responses to the drugs used in the present study may explain the maintenance of venous return due to prevention of portal vein pressure rise when Phb. is administered before endotoxin.
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