[Stimulation of ciliary motility by beta 3-adrenoceptor agonist rabbit tracheal epithelium]

To determine whether atypical beta-adrenoceptor (beta 3-adrenoceptor) agonist, BRL 37344, stimulates airway ciliary motility and, if so, what its mechanism of action is, we studied rabbit tracheal epithelium in vitro. Epithelial cells cultured for 7 days were mounted in the Rose chamber and ciliary beat frequency (CBF) was measured by a photoelectric method. Addition of BRL 37344 rapidly increased CBF from 15.5 +/- 0.6 to 20.3 +/- 1.4 Hz (mean +/- SE, p < 0.01), which remained elevated for at least 20 min. This effect was concentration-dependent, the maximal increase from the baseline value and the EC50 being 27.2 +/- 0.4% (mean +/- SE, p < 0.01) and 1.75 x 10(-7) M, respectively. Other beta-adrenoceptor agonists likewise increased CBF, where the rank order of potency was salbutamol (1) > BRL 37344 (0.57) >> norepinephrine (1.3 x 10(-3)). Preincubation of cells with propranolol inhibited the increase in CBF produced by salbutamol, and BRL 37344 significantly raised intracellular cyclic AMP contents. These results suggest that beta 3-adrenoceptor probably exists in rabbit tracheal epithelium and that stimulation of this type of receptor increases ciliary motility through a cyclic AMP-dependent mechanism, an effect that might be of value in enhancing mucociliary transport function in the airway.