Influence of fenoldopam and quinpirole in the guinea-pig stomach.
1. The influence of the selective DA1-agonist fenoldopam and the selective DA2-agonist quinpirole was investigated in the guinea-pig intact stomach model and in guinea-pig gastric corpus muscle strips. 2. In the intact stomach model, quinpirole induced a relaxation from 10(-6) M on. The relaxation by quinpirole (3 x 10(-5) M) was significantly inhibited by rauwolscine (10(-7) M), yohimbine (10(-7) M) and domperidone (10(-6) M). In the presence of tetrodotoxin, quinpirole (3 x 10(-5) M) induced a contraction. 3. In the same model, fenoldopam induced a relaxation but only at 3 x 10(-5) M. The relaxation by fenoldopam (3 x 10(-5) M) was not inhibited by SCH 23390 (10(-6) M). The relaxant effect of dopamine (3 x 10(-6) M) was significantly inhibited by rauwolscine (10(-7) M), yohimbine (3 x 10(-7) M), haloperidol (10(-6) M) and domperidone (10(-6) M). 4. In circular muscle strips of the gastric corpus, the electrically induced cholinergic contractions were inhibited by dopamine but not consistently influenced by quinpirole or fenoldopam. 5. Dopamine, fenoldopam and quinpirole induced an increase in basal tone of the strips. The contraction by dopamine (10(-5) M) was significantly antagonized by prazosin and methysergide. 6. No evidence was thus found for the presence of DA1-receptors in both guinea-pig stomach models. Equally, no evidence for the presence of DA2-receptors was found when studying quinpirole in the strips. Although the relaxant effect of quinpirole in the intact stomach seems predominantly mediated via alpha 2-adrenoceptors, an involvement of DA2-receptors cannot be excluded.
Heymans Institute of Pharmacology, University of Gent Medical School, Belgium.
F
F
Guenaneche
J A
JA
Schuurkes
R A
RA
Lefebvre
D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D015259:Dopamine Agents / Q000494:pharmacology*; D004558:Electric Stimulation; D004873:Ergolines / Q000494:pharmacology*; D005260:Female; D018818:Fenoldopam; D006168:Guinea Pigs; D006220:Haloperidol / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D011224:Prazosin / Q000494:pharmacology; D019257:Quinpirole; D013270:Stomach / Q000187:drug effects* / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
D015259:Dopamine Agents; D004873:Ergolines; D019257:Quinpirole; D015016:Yohimbine; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D018818:Fenoldopam; D006220:Haloperidol; D003000:Clonidine; D004298:Dopamine; D011224:Prazosin; D008784:Methysergide