Vascular Anti‐permeability Effects of β‐receptor Agonists and Theophylline in the Lung

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Abstract
In conscious guinea‐pigs the effect of theophylline, terbutaline and isoprenaline on histamine‐induced increase in lung weight was examined. Animals exposed to a saline aerosol had a lung weight to body weight ratio of about 0.8 %. Exposure to a histamine aerosol raised this value to about 1.1(P <0.001). Theophylline 55 mg/kg and 110 mg/kg was given orally, terbutaline 0.1 mg/kg and isoprenaline 0.01 mg/kg and 0.03 mg/kg subcutaneously before exposure to histamine. The three drugs prevented the lung weight effect produced by histamine aerosol (P<0.01, P<0.001, P<0.001, P<0.1, P<0.001 respectively). Changes in lung blood content did not contribute to the weight‐reducing effects. The potency ratio found between terbutaline and isoprenaline suggests that β‐2‐receptors might be involved in the anti‐permeability effect. Propranolol‐treated animals did not survive in the histamine‐aerosol unless they received theophylline; neither bronchodilator nor anti‐permeability effects of theophylline were antagonized by propranolol. It is concluded that in guinea‐pigs theophylline and β‐agonists, in bronchodilating doses have the additional effect of preventing permeability oedema in the lung.