Postjunctional α2-adrenoceptors in blood vessels of human nasal mucosa

Summary Human nasal mucosa has various types of blood vessels and is a good tissue for demonstrating receptors for many vasoactive substances, including -adrenoceptors. In contrast to the large contractile response induced by ₂-agonists, our studies have shown that ₂-agonists produce a small maximal contraction. This ₂-induced response was easily blocked by ₁-antagonists, indicating that it is evoked, at least partially, by the stimulation of ₁-adrenoceptors. Noradrenaline (NA)-induced contractions could not be abolished by either ₁- or ₂-antagonists alone, but were almost completely blocked by the combination of both antagonists. This suggests the presence of postjunctional ₂-adrenoceptors. The low-maximal responsiveness to ₂-agonists and calcium independency of NA-induced contractions were distinct from our former results obtained on canine nasal specimens.