Naloxone antagonism of phenoxybenzamine antinociception in the mouse tail stimulation test. |
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Authors: | V R Spiehler L Paalzow |
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Affiliation: | Department of Pharmacology, Central Research and Control Laboratory of the National Corporation of Swedish Pharmacies, Box 3045, S-171 03 Solna, Sweden |
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Abstract: | Phenoxybenzamine was antinociceptive in the mouse tail electrical stimulation assay (ED50, 36.8 mg/kg) with a peak effect at hours after subcutaneous injection. Naloxone antagonized this antinociception action of phenoxybenzamine in a dose-related manner. Dose-ratio analysis of naloxone's antagonism of phenoxybenzamine antinociception gave a pA2 value of 6.15, similar to that found for the benzomorphinan mixed agonist-antagonists. This is in agreement with the sodium response ratio found for phenoxybenzamine, 4.3, in assays of phenoxybenzamine inhibition of 3H-naloxone binding to mouse brain homogenate (5). These findings suggest that phenoxybenzamine binds to the opiate receptor both as well as in a manner similar to the mixed agonist-antagonists. |
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