| Abstract: | Dopamine and phenylephrine decreased the tone of the smooth muscles of the isolated rat stomach strips in concentractions of 10(-6) M and higher. The curves of the concentration-effect have the same slope. Dopamine effects are unchanged in the presence of propranolole (5.10(-6) g/ml). Phentholamine (as well as dihydroergotamine and tropaphen) shows an equal degree of antagonism towards both phenylephrine and dopamine. It is suggested that dopamine and phenylephrine relax the stomach muscles by influencing the alpha-adrenoreceptors. The latter differe from alpha-adrenoreceptors of the ejaculatory duct of rats by a high sensitivity to the blocking influence of some neuroleptics--haloperidol, trifluoperazine, chlorpromazine, pA2 for which (8.11--8.64) is of the same range as pA2 for alpha-adrenolytic drugs (7.76--8.46). The features of resemblance and difference between alpha-adrenoreceptors of the gastrointestinal tract muscles and the inhibitory dopamine receptors of the nerve cells are being discussed. |
