The in vitro effects of the nitric oxide (NO) substrate L-arginine on ciliary beat frequency and the in vivo effects of the NO donor sodium nitroprusside (SNP) on mucociliary activity were investigated in the rabbit maxillary sinus mucosa with photoelectric techniques. L-Arginine increased ciliary beat frequency in vitro with a maximum response of 27.1% +/- 6.4% at 10(-3) mol/L, and this effect was reversibly blocked by pretreatment with the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine, whereas D-arginine had no such effect. SNP increased mucociliary activity in vivo, the peak response of 36.8% +/- 4.2% being obtained at the dose of 30.0 microg/kg. No tachyphylaxis was observed after repeat challenge with SNP. The increase in mucociliary activity caused by SNP was largely unaffected by pretreatment with the calcium channel blocker nifedipine, the cyclooxygenase inhibitor diclofenac, and the cholinergic antagonist atropine. The nonselective beta-blocker propranolol delayed the peak response of SNP to 7 to 8 minutes after challenge, compared with 1 to 2 minutes after challenge in animals without pretreatment. The results show the NO substrate L-arginine and the NO donor SNP to have ciliostimulatory effects in vitro and in vivo, respectively. The occurrence of NOS production in the sphenopalatine ganglion and sinus mucosa of the rabbit was studied by immunohistochemistry for NOS activity or nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry. The latter is an indirect sign of neuronal NOS activity. Numerous NOS-containing cell bodies were seen in the sphenopalatine ganglion; in the sinus mucosa a moderate supply of thin NOS-immunoreactive nerve fibers was seen. Taken together, the morphologic findings and the functional results indicate NO to be a regulator of mucociliary activity in upper airways.