In cats anaesthetized with pentobarbitone sodium (45 mg kg-1), electrical stimulation of the parasympathetic nerve fibres to the nasal mucosa evoked frequency-dependent increases in nasal arterial blood flow whereas stimulation of the superior cervical sympathetic nerve induced marked vasoconstriction. 2. Sympathetic nerve stimulation for 3 min at 10 Hz evoked significant (P < 0.05) and prolonged (> 30 min) attenuation of the vasodilatory response to subsequent parasympathetic stimulation. 3. Combined pretreatment with adrenergic and cholinergic blockers reduced the vasoconstrictory effect of sympathetic stimulation by 28 +/- 4% (mean +/- S.E.M.) and the parasympathetically evoked vasodilatation by 20 +/- 5%. 4. The vasodilatory effects of exogenous vasoactive intestinal polypeptide, peptide histidine isoleucine and galanin, and the vasoconstrictory effects of exogenous neuropeptide Y (NPY) and alpha,beta-methylene adenosine 5'-triphosphate were not altered by adrenoceptor antagonists and atropine whereas the effects of exogenous noradrenaline and acetylcholine were virtually abolished. 5. The atropine-resistant parasympathetic vasodilatation remained significantly attenuated for more than 30 min after the non-adrenergic sympathetically evoked vasoconstriction. 6. Exogenous NPY (25 x 10(-9) mol) mimicked the effect of sympathetic stimulation in attenuating subsequent parasympathetically evoked vasodilatation.
