β‐ADRENOCEPTOR MEDIATED INHIBITION BY TERBUTALINE OF HISTAMINE EFFECTS ON VASCULAR PERMEABILITY

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Abstract
1 In guinea-pigs, previously given Evans blue dye intravenously, 13 to 18 intradermal injections of histamine, with or without other drugs, were made into the depilated trunk skin. Dye was then quantitatively extracted from each skin area and the measured absorbance values were used as a measure of vascular leakage of macromolecules. 2 Histamine (0.5 to 12 nmol) produced dose-related increases in vascular leakage. These were reduced by terbutaline (1 and 10 nmol) which produced a significant shift in the histamine dose-response lines to lower absorbance values. The effect of 0.1 nmol of terbutaline was significant only against doses of histamine of less than 2 nmol. 3 Propranolol (1 nmol and 10 nmol) antagonized the effects of terbutaline. Propranolol, at a dose of 10 nmol but not 1 nmol, itself reduced the responses to 1.5 nmol histamine. 4 We conclude that the inhibition by terbutaline of histamine-induced dye leakage in guinea-pig skin is mediated by stimulation of β-adrenoceptors and it is suggested that this effect of terbutaline occurs directly on β-receptors at the vascular leakage site.