Alpha 1-receptors at pre-capillary resistance vessels of the human nasal mucosa.

The aim of the present study was to further characterise the alpha-adrenoceptors in pre-capillary arteries of the human nasal mucosa. Mucosa was obtained from patients undergoing endonasal surgery. From the isolated conchae small arteries (diameter: 90-220 microns) were dissected, avoiding any direct traumatisation. The arteries were mounted to a Mulvany-Halpern wire myograph allowing isometric registration of the vessel constriction. Receptor subtypes were characterised using the agonists noradrenaline, phenylephrine and oxymetazoline, and the antagonists prazosine and yohimbine. The EC50 values of the three agonists were in the micromolar range, whereas the Emax values differed. When maximal responses to the agonists were expressed as a percentage of a potassium-induced constriction, values for noradrenaline, phenylephrine and oxymetazoline amounted to 110%, 78% and 21%, respectively. The agonist effects were almost completely blocked by the alpha 1-receptor antagonist prazosine, whereas yohimbine, the alpha 2-receptor antagonist, did not affect the agonist responses. From these results it is concluded that the adrenoceptors in pre-capillary arteries of the mucosa in human central concha are of the alpha-type. Since the decongestive effect of alpha 2-receptor agonists is beyond any doubt, this subtype of the adrenoceptor must be present on the venous capacitance vessels.