Dual histamine receptor mechanism in guinea-pig lung.
Isolated guinea-pig lung parenchymal strips (GPLS) relaxed in response to the selective histamine H2-receptor agonists, dimaprit and 4-methylhistamine (4-MeH), and to low doses of histamine (10(-9) to 10(-7) mol/l) and contracted in response to several spasmogens. The order of the relative activity of the spasmogens was 2-methylhistamine (2-MeH) greater than histamine greater than carbachol greater than 2-pyridylethylamine (2-PE). Dimaprit and 4-MeH also relaxed GPLS which were contracted by 2-MeH, 2-PE or carbachol. Metiamide (a selective H2-antagonist: 5 x 10(-5) mol/l inhibited or reversed relaxations to histamine, dimaprit and 4-MeH, and significantly enhanced contractile responses to histamine without altering responses to carbachol. Mepyramine (a selective H1-receptor antagonist: 10(-8) to 10(-6) mol/l antagonized histamine-induced contractions. This investigation shows: (1) histamine is more active than carbachol in GPLS and (2) the occurrence of histamine H1-receptors mediating contraction and H2-receptors mediating relaxation in guinea-pig lung.
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D005021:Ethylamines / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006635:Histamine H2 Antagonists / Q000494:pharmacology; D008168:Lung / Q000187:drug effects / Q000294:innervation*; D008297:Male; D008761:Methylhistamines / Q000494:pharmacology; D008785:Metiamide / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects; D011968:Receptors, Histamine / Q000187:drug effects*; D011969:Receptors, Histamine H1 / Q000187:drug effects*; D011970:Receptors, Histamine H2 / Q000187:drug effects*
D005021:Ethylamines; D006634:Histamine H1 Antagonists; D006635:Histamine H2 Antagonists; D008761:Methylhistamines; D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D008785:Metiamide; D006632:Histamine; D002217:Carbachol