alpha(2)-Adrenoceptor and NPY receptor-mediated contractions of porcine isolated blood vessels: evidence for involvement of the vascular endothelium

1 Enhanced contractions to the alpha(2)-adrenoceptor agonist UK14304 and ne uropeptide Y (NPY) in the porcine ear artery can be uncovered by pharmacolo gical manipulation. The aim of this study was to determine whether similar pharmacological manipulation can uncover enhanced contractions in the porci ne splenic artery, and to determine whether the endothelium modulates these responses. 2 UK14304 (0.3 mu M) and NPY (0.1 mu M) produced small contractions of the porcine splenic artery. After pre-contraction of the tissue with U46619, fo llowed by relaxation with forskolin, the responses to both UK14304 and NPY were enhanced. Enhanced contractions to both UK14304 and NPY were also obta ined after relaxation with SNP. These results demonstrate that, as in the p orcine ear artery, alpha 2-adrenoceptors and NPY receptors are able to prod uce enhanced contractile responses through both adenylyl cyclase-dependent and -independent signal transduction pathways. 3 Removal of the endothelium had no significant effect on responses to UK14 304 either alone or in the presence of U46619 and forskolin in the porcine splenic artery. On the other hand, responses to UK14304 after relaxation wi th SNP were reduced after endothelium-denudation in both the porcine spleni c artery and ear artery. Similar results were obtained with NPY in the porc ine ear artery. 4 In conclusion, enhanced contractile responses to UK14304 and NPY in the p orcine splenic artery can be uncovered using methods similar to those emplo yed in the porcine ear artery. Under certain conditions the responses to bo th agents are modulated by the endothelium. These data highlight further th e similarities in the signal transduction pathways used by both alpha(2)-ad renoceptors and NPY receptors to induce vasoconstriction.