1. We have studied the effect of the anti-inflammatory anti-asthma drug, nedocromil sodium, on down-regulation of pulmonary β-adrenoceptors in guinea-pig lung.

2. Incubation of minced lung with isoprenaline (10 μmol/l) resulted in a reduction in maximum binding capacity of [125I]iodocyanopindolol to lung membranes from 246 ± 4 to 169 ± 6 fmol/mg of protein (mean ± sem, P < 0.01, n = 18).

3. Nedocromil sodium, which had no direct effect on [125I]iodocyanopindolol binding, prevented isoprenaline-induced down-regulation, giving complete protection at a dose of 100 μmol/l.

4. The mechanism of this effect is not certain, but nedocromil sodium may interfere with the internalization of β-adrenoceptors in pulmonary parenchymal cells. This may have some therapeutic relevance.

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