Dopamine and the depressant action of morphine on stimulated guinea-pig ileum.
1 Morphine reduces the amplitude of the contractions induced by electrical stimulation, in the myenteric plexus-longitudinal muscle preparation of guinea-pig ileum. Dopamine and apomorphine have the same effect but at much higher concentrations. 2 Dopamine, at concentrations lower than those which would normally be inhibitory, partially reverses the depressant effect of morphine. 3 Pre-treatment of guinea-pigs with 6-hydroxydopamine results in a slight supersensitivity of innervated longitudinal muscle preparations to dopamine and has no effect on morphine activity. 4 Naloxone antagonizes the depressant effect of morphine but not that of dopamine or apomorphine. 5 The response of theileum preparation to morphine is not affected by phentolamine or propranolol; the effect of dopamine, however, is abolished by alpha-adrenoceptor blockade.
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology*; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D006892:Hydroxydopamines / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology
D006892:Hydroxydopamines; D009270:Naloxone; D009020:Morphine; D011433:Propranolol; D001058:Apomorphine; D004298:Dopamine; D010646:Phentolamine