The permeability of respiratory mucosa, as measured by clearance of diethylenetriamine penta-acetate (DTPA) labelled with technetium 99m, was similar in seven normal and nine asthmatic subjects. Histamine induced bronchoconstriction was associated with a 50% increase in permeability in both groups of subjects. In normal subjects inhaled salbutamol, given as 1 mg acutely or as 200 micrograms four times daily for two weeks, had no effect on pulmonary permeability. Salbutamol, given before histamine challenge, prevented bronchoconstriction, but did not affect the increase in permeability seen in normal subjects. Low doses of histamine, sufficient to cause bronchoconstriction in the asthmatic subjects, produced little bronchoconstriction in normal subjects but caused increases in lung permeability similar to those seen in asthmatic subjects. These studies suggest that these two effects of inhaled histamine, bronchoconstriction and increased permeability, are independent.
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