TY - JOUR
T1 - Mechanisms of α-adrenoceptor mediated contractions of rat mesenteric artery
AU - Kannan, M. S.
AU - Seip, A. E.
PY - 1986
Y1 - 1986
N2 - The nature of the calcium channels associated with the activation of alpha-adrenoceptors in vascular smooth muscle has been investigated. The inhibitory effects of nitrendipine, a calcium antagonist, were studied on the contractions elicited by α-adrenoceptor agonists in rat superior mesenteric artery. Responses to equieffective concentrations of phenylephrine (α1-adrenoceptor agonist), clonidine and BHT-920, (α2-adrenoceptor agonists), and noradrenaline (nonselective agonist) were inhibited differentially by the calcium antagonist, with the sensitivity order being as follows: BHT-920 = clonidine > phenylephrine > noradrenaline. When the contractions to two doses of noradrenaline were compared, the low dose response was more sensitive to nitrendipine inhibition than the high dose response. This differential inhibition was not seen for noradrenaline in the presence of verapamil or for phenylephrine in the presence of nitrendipine. The contractions of the vessel to the agonists in zero calcium conditions were not significantly different from each other. The sensitivity differences among the agonists to nitrendipine may arise from differences in the postreceptor mechanisms of activation. The differential sensitivity of noradrenaline responses suggests a greater heterogeneity of calcium channels than those available for the other agonists.
AB - The nature of the calcium channels associated with the activation of alpha-adrenoceptors in vascular smooth muscle has been investigated. The inhibitory effects of nitrendipine, a calcium antagonist, were studied on the contractions elicited by α-adrenoceptor agonists in rat superior mesenteric artery. Responses to equieffective concentrations of phenylephrine (α1-adrenoceptor agonist), clonidine and BHT-920, (α2-adrenoceptor agonists), and noradrenaline (nonselective agonist) were inhibited differentially by the calcium antagonist, with the sensitivity order being as follows: BHT-920 = clonidine > phenylephrine > noradrenaline. When the contractions to two doses of noradrenaline were compared, the low dose response was more sensitive to nitrendipine inhibition than the high dose response. This differential inhibition was not seen for noradrenaline in the presence of verapamil or for phenylephrine in the presence of nitrendipine. The contractions of the vessel to the agonists in zero calcium conditions were not significantly different from each other. The sensitivity differences among the agonists to nitrendipine may arise from differences in the postreceptor mechanisms of activation. The differential sensitivity of noradrenaline responses suggests a greater heterogeneity of calcium channels than those available for the other agonists.
UR - http://www.scopus.com/inward/record.url?scp=0022922587&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0022922587&partnerID=8YFLogxK
U2 - 10.1139/y86-067
DO - 10.1139/y86-067
M3 - Article
C2 - 2873878
AN - SCOPUS:0022922587
SN - 0008-4212
VL - 64
SP - 419
EP - 423
JO - Canadian Journal of Physiology and Pharmacology
JF - Canadian Journal of Physiology and Pharmacology
IS - 4
ER -