Tyramine antagonizes proctolin-induced contraction of the isolated foregut of the locust Schistocerca gregaria by an interaction with octopamine2 receptors.
1. Octopamine (OA) (10(-7)-10(-5) M) relaxed isolated foreguts. Tyramine mimicked the effects of OA but was 64x less potent. 2. Proctolin (10(-8) M to 10(-6) M) induced contraction of isolated foreguts was antagonised non competitively by tyramine. 3. Mianserin (10(-6) M) was a non competitive antagonist of relaxation caused by tyramine but was without effect on proctolin induced contraction. 4. Caffeine (1 microM and 2 microM) caused non competitive inhibition of proctolin-induced tissue contraction. 5. It is concluded that tyramine antagonises proctolin-induced contraction of the foregut by activating an adenylate cyclase-linked OA2 receptor.
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SE
Beecham Pharmaceuticals, Medicinal Research Centre, Harlow, Essex, U.K.
Wood
S J
SJ
Osborne
R H
RH
Cattell
K J
KJ
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D004064:Digestive System / Q000187:drug effects*; D004068:Digestive System Physiological Phenomena; D004305:Dose-Response Relationship, Drug; D005260:Female; D006110:Grasshoppers / Q000502:physiology*; D008297:Male; D008803:Mianserin / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009479:Neuropeptides; D009655:Octopamine / Q000494:pharmacology; D009842:Oligopeptides / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000378:metabolism*; D017982:Receptors, Biogenic Amine; D014439:Tyramine / Q000494:pharmacology*
D009479:Neuropeptides; D009842:Oligopeptides; D011941:Receptors, Adrenergic; D017982:Receptors, Biogenic Amine; C027604:norsynephrine receptor; D009655:Octopamine; D008803:Mianserin; D002110:Caffeine; C011536:proctolin; D014439:Tyramine