An evaluation of the ability of a series of full alpha-1 adrenoceptor agonists to release internal calcium in venous smooth muscle.
Our previous studies have shown that activation of postsynaptic alpha-2 adrenoceptors mainly utilizes extracellular calcium whereas activation of postsynaptic alpha-1 adrenoceptors mobilizes both extracellular and intracellular calcium to produce contractions in the canine saphenous vein. In the present study, the abilities of several full alpha-1 adrenoceptor agonists to release internal calcium for contractions in the canine saphenous vein were evaluated. Contractions to these alpha-1 agonists at two different equieffective concentrations (concentrations that produced 50 and 80% of the maximum phenylephrine response, PE50 and PE80, respectively) were determined in both zero external calcium medium and in normal calcium medium containing 5 mM La . If a correlation exists between the efficacy of an agonist and its ability to release internal Ca++, the contractile response to each agonist should be similar under these conditions. The results indicated marked variations in mechanical responses elicited by these alpha-1 agonists at both PE50 and PE80 concentrations. The data suggest a lack of correlation between efficacy and the ability to release internal calcium to induce contractions for a series of full alpha-1 adrenoceptor agonists in venous smooth muscle.
Jim
K F
KF
Macia
R A
RA
Matthews
W D
WD
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003470:Culture Media; D004285:Dogs; D007093:Imidazoles / Q000494:pharmacology; D007811:Lanthanum / Q000378:metabolism; D008433:Mathematics; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D010627:Phenethylamines / Q000494:pharmacology; D010656:Phenylephrine / Q000031:analogs & derivatives / Q000494:pharmacology; D012501:Saphenous Vein; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D003470:Culture Media; D007093:Imidazoles; D010627:Phenethylamines; D013764:Tetrahydronaphthalenes; D010656:Phenylephrine; D007811:Lanthanum; C049130:SK&F 29029; C039140:SK&F 89748; C044512:SK&F 102652; C014282:cirazoline; D002118:Calcium