ISSN:
1420-908X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract H1-receptor reserves in guinea-pig left atria, trachea and pig coronary arteries were calculated by the use of phenoxybenzamine (Pba), a β-haloalkylamine that irreversibly blocks the H1-receptor response to histamine or 2-(2-pyridyl)-ethylamine (PEA). Equieffective concentrations of the H1-agonist in the absence (A) and presence (A′) of Pba were evaluated from concentration-response curves. By plotting the reciprocal values 1/A versus 1/A′ the amount of H1-receptors not occupied by the agonist was calculated. The size of the H1-receptor reserve could be estimated by comparison of the receptor occupation with the corresponding effect. Furthermore, the dissociation constants for histamine, PEA, Pba and the pD′2-values for Pba were determined for the different tissues. 5% and 6% H1-receptor occupation is necessary to achieve a half maximal contraction of the trachea with the agonists histamine and PEA, respectively. Only 0.5% H1-receptor occupation is needed for the half maximal positiv inotropic effect of histamine in left atria, while 5.5% of the H1-receptors have to be accupied using PEA as an agonist in this tissue. In the coronary artery of the pig 50% of the maximal contraction can be achieved by stimulation of 15.1% of the H1-receptors with histamine.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01967405
