Occurrence of inhibitory histamine H2-receptors in isolated pulmonary blood vessels of dogs and rats

Summary Isolated, helically cut strips of pulmonary arteries and veins of dogs, and pulmonary arteries of rats, precontracted with norepinephrine or 5-HT exhibited potent concentration-dependent relaxations to impromidine and dimaprit (histamine H₂-agonists). The occurrence of inhibitory histamine H₂-receptors in the pulmonary vasculature could play a modulatory role in hypoxic pulmonary vasoconstriction.Supported by research grants NHLBI-18002, NHLBI-18015 and DA-02339 from the USPHS. We are grateful to Dr D.D.A. Owen of Smith, Kline & French Ltd, England for the generous supply of dimaprit and impromidine. Requests for reprints should be addressed to B.M. Altura.