Effect of dopamine on smooth muscles of the rat stomach and characteristics of ? adrenoreceptors of muscle cells of the gastrointestinal tract

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Abstract
Dopamine and phenylephrine lower the tone of the smooth muscles of isolated strips of rat stomach in concentrations of 10−6M or more. The concentration-effect curves have the same slope. The effect of dopamine is unchanged in the presence of propranolol (5·10−6 g⩳). Phentolamine (and also dihydroergotamine and tropaphen) exhibits equal antagonism to phenylephrine and dopamine. It is concluded that dopamine and phenylephrine relax the smooth muscles of the stomach by their action on α adrenoreceptors. The latter differ from the α adrenoreceptors of the vas deferens (rats) in their high sensitivity to the blocking effect of certain neuroleptics, namely haloperidol, trifluoroperazine, and chlorpromazine, pA2 for which (8.11–8.64) is of the same order as pA2 for α adrenolytics (7.76–8.46). The similarity and difference between α adrenoreceptors of muscles of the gastrointestinal tract and inhibitory dopaminergic receptors of nerve cells are discussed.