The effect of noradrenaline on mucociliary activity in the rabbit maxillary sinus
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The effect of noradrenaline (NA) on mucociliary activity in the rabbit maxillary sinus was investigated in vivo by injecting it at increasing dosages (10(-11) to 10(-4) mol/kg) into the maxillary artery, the mucociliary response being recorded photoelectrically. NA increased mucociliary activity at a dosage of 10(-5) mol/kg, the maximal increase being 16.1 +/- 2.6%. The NA-induced stimulation of mucociliary activity had a latency of 20 s, and the activity returned to base-line level within 3 min. Pretreatment with the alpha-antagonist phentolamine (0.2 and 1.0 mg/kg) or the cholinergic antagonist atropine (1 mg/kg) did not alter mucociliary response to NA. Blockade with the beta-antagonist propranolol did not significantly reduce the maximal response to NA, which was 16.1 +/- 2.6% before and 11.1 +/- 3.0% after pretreatment with propranolol (n = 7; p = 0.2). In contrast, pretreatment with the prostaglandin-synthesis inhibitor indomethacin reduced the response from 12.9 +/- 2.9% to 6.3 +/- 1.3% (n = 6; p < 0.05), suggesting that at high dosages NA stimulates mucociliary activity via the cyclo-oxygenase pathway.