Effect of sodium metabisulphite on bronchial blood flow in conscious sheep: pharmacological modulation.

1. Sodium metabisulphite (MBS) can induce bronchoconstriction in patients with asthma. We investigated the effects of MBS aerosol on bronchial blood velocity (Vbr) and pulmonary resistance in intubated conscious sheep. 2. Bronchial blood velocity was measured by implanting a 20 MHz ultrasonic Doppler flow probe on the common bronchial branch of the bronchoesophageal artery. 3. Inhaled MBS induced a dose-dependent, transient increase in Vbr lasting for a few minutes without any changes in aortic and pulmonary artery pressures. There was some tachyphylaxis of the Vbr response to successive inhalations of MBS. 4. The cholinoceptor antagonist, ipratropium bromide and the H1 and H2 histamine antagonists, chlorpheniramine and cimetidine, had no significant effect on MBS-induced increase on Vbr. The loop diuretic, frusemide, and the anti-inflammatory drug, nedocromil sodium, which both inhibit MBS-induced bronchoconstriction in patients with asthma, were also without effect. 5. We conclude that MBS induces bronchial vasodilatation in conscious sheep, and that this effect is not dependent on the release of histamine or other mediators, or an activation of cholinergic pathways.