title: Effects of histamine bolus injections and continuous infusions on the H1- and H2-receptors in the hindlimb vessels of the rabbit.
abstract: 1. Hindlimb vascular resistance (HVR) was continuously measured after pharmacological block of the autonomic effectors in unanesthetized rabbits with previously implanted Doppler ultrasonic flowmeters. 2. Histamine bolus injections caused a dose-related short lived fall in HVR followed by a more sustained rise. The fall was due to H2-receptor stimulation (blocked by burimamide or metiamide) and the rise to H1-receptor stimulation (blocked by mepyramine). At the doses of histamine tested the magnitude of the H1-mediated vasoconstriction had a larger peak effect than the H2-mediated vasodilatation. 3. Histamine infusions up to 200 microgram kg-1 min-1 did not alter HVR significantly but both increases and decreases in HVR were observed after giving H2- or H1-antagonists, respectively. 4. From the double reciprocal plots of 1/peak HVR change and 1/dose of histamine the magnitude of the predicted H1- and H2-mediated peak HVR effects at large doses were the same. This suggested that the number of H1- and H2-receptors were similar in the hindlimb vascular bed, in agreement with the infusion data.
mesh_terms: D000818:Animals; D001340:Autonomic Nerve Block; D002049:Burimamide / Q000494:pharmacology; D004347:Drug Interactions; D006614:Hindlimb / Q000098:blood supply; D006632:Histamine / Q000008:administration & dosage / Q000494:pharmacology*; D007263:Infusions, Parenteral; D007275:Injections, Intravenous; D007700:Kinetics; D008297:Male; D008785:Metiamide / Q000494:pharmacology; D011738:Pyrilamine / Q000494:pharmacology; D011817:Rabbits; D011968:Receptors, Histamine / Q000187:drug effects*; D011969:Receptors, Histamine H1 / Q000187:drug effects*; D011970:Receptors, Histamine H2 / Q000187:drug effects*; D012039:Regional Blood Flow / Q000187:drug effects; D013997:Time Factors; D014655:Vascular Resistance / Q000187:drug effects; D014666:Vasomotor System / Q000187:drug effects*
chemical_list: D011968:Receptors, Histamine; D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D008785:Metiamide; D006632:Histamine; D011738:Pyrilamine; D002049:Burimamide