In vitro study of the influence of dopamine on rat and dog gastric fundus.
The effect of dopamine was studied in rat longitudinal fundus strips and in dog circular and longitudinal fundus strips. Contractions of similar amplitude were induced by transmural stimulation and by methacholine. In the rat, dopamine inhibits the electrically induced contractions partially by a post-junctional influence on the smooth muscle cells and partially by inhibiting the release of acetylcholine from the intramural cholinergic neurons. The latter effect is antagonized by phentolamine, while the former is antagonized by propranolol. Dopamine antagonists change the inhibitory effect of dopamine to a small degree but have a similar influence on the inhibitory effect of noradrenaline. The inhibitory effect of dopamine is largely indirect through the liberation of noradrenaline, since in the presence of cocaine or after reserpine-pretreatment the inhibition by dopamine is markedly reduced. In the presence of propranolol, cocaine and hydrocortisone, the inhibitory effect of dopamine is equally antagonized by the alpha 1-antagonist prazosin and the alpha 2-antagonist rauwolscine. In the dog, the inhibition of the electrically induced contractions by dopamine is mainly due to inhibition of the release of acetylcholine from the intramural cholinergic neurons. This effect is not influenced by the presence of cocaine and is completely antagonized by phentolamine and rauwolscine, while prazosin has no effect. From the dopamine antagonists tested, only metoclopramide had some antagonistic effect against dopamine but it antagonized to the same degree the inhibition by noradrenaline.
D000818:Animals; D004285:Dogs; D004298:Dopamine / Q000494:pharmacology* / Q000502:physiology; D018492:Dopamine Antagonists; D004558:Electric Stimulation; D005748:Gastric Fundus / Q000187:drug effects*; D066298:In Vitro Techniques; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D051381:Rats
D018492:Dopamine Antagonists; D008688:Methacholine Compounds; D016210:Methacholine Chloride; D004298:Dopamine