Sympathetic vascular control of the pig nasal mucosa: adrenoceptor mechanisms in blood flow and volume control.

1. The adrenoceptor mechanisms influencing the total blood flow, volume and superficial blood flow in the nasal mucosa of pigs anaesthetized with pentobarbitone have been characterized by use of various agonists and antagonists. 2. Local intra-arterial bolus injection of the selective alpha 1-agonist phenylephrine, the selective alpha 2-agonist UK 14.304, the mixed alpha 1/alpha 2-agonist oxymetazoline and the mixed alpha/beta-agonists noradrenaline (NA) and adrenaline induced dosed-related reduction of nasal arterial blood flow (BF), nasal mucosal volume (V, reflecting capacitance vessel function) and the laser Doppler flowmetry signal (LDF, reflecting superficial movement of blood cells). The rank order of alpha-agonist potency regarding BF reduction was UK 14.304 greater than oxymetazoline greater than phenylephrine = adrenaline. For the volume response the potency order was UK 14.304 greater than oxymetazoline = NA = adrenaline greater than phenylephrine while for the reduction of the LDF signal the potency was UK 14.304 = NA = adrenaline greater than oxymetazoline greater than phenylephrine. The selective beta 2-agonist terbutaline caused dose-dependent increase of BF whereas only a small augmentation of the V was obtained upon the highest dose (40 nmol) while no modification of the LDF signal was observed. 3. After pretreatment with the selective alpha 1-antagonist prazosin, the response to phenylephrine was abolished while the selective alpha 2-antagonist idazoxan attenuated the effect of UK 14.304. After pretreatment with alpha-antagonists, both NA and adrenaline caused biphasic effects with constriction followed by vasodilatation for BF, but not for V or LDF. This vasodilatation was blocked by the beta-antagonist propranolol. 4. The reduction in nasal BF and V upon sympathetic nerve stimulation was attenuated both by prazosin and idazoxan. Propranolol enhanced the remaining reduction of BF but not of V in the presence of alpha-antagonists. 5. It is concluded that alpha 2-adrenoceptor mechanisms in the pig nasal mucosa are dominating for the BF, V and LDF responses to exogenous agonists. alpha 1-Adrenoceptors also seem to be involved in the sympathetic control of BF, V and LDF. Activation of beta 2-receptors increases mainly BF and does not influence the LDF signal.