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Phentolamine lacks α 2 ‐adrenoceptor agonist activity in anaesthetized dogs
Author(s) -
Bell C.
Publication year - 1988
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1988.tb11439.x
Subject(s) - phentolamine , yohimbine , vasoconstriction , hexamethonium , endocrinology , medicine , clonidine , agonist , blockade , chemistry , anesthesia , antagonist , stimulation , receptor
1 This study was performed in order to determine whether the blockade of sympathetic vasoconstriction in anaesthetized dogs by phentolamine is due to the antagonist action of the drug at postjunctional adrenoceptors, or is due to depression of neurotransmitter release by an agonist action at prejunctional adrenoceptors. 2 In dogs made areflexic by ganglion blockade with hexamethonium, phentolamine (0.5 mg i.a. or 0.5 mg kg −1 i.v.) elevated or did not affect femoral blood flow. By contrast, clonidine (0.5‐2.5 nmol, i.a.) produced femoral vasoconstriction, which was attenuated by prior administration of phentolamine. 3 Prior blockade of prejunctional α 2 ‐adrenoceptors with yohimbine (30 μg kg −1 , i.v.) did not reduce the blocking effect of phentolamine (0.5 mg kg −1 , i.v.) on neurogenic vasoconstriction. 4 The results indicate that, in anaesthetized dogs, phentolamine lacks appreciable agonist activity at either prejunctional or postjunctional α 2 ‐adrenoceptors. The blockade of neurogenic responses by phentolamine is therefore likely to be due to postjunctional adrenoceptor blockade.