Effects of nifedipine on phasic and tonic vasoconstrictor responses to Sgd 101/75 in the isolated perfused rabbit ear artery.
The relative importance of extracellular Ca2+ influx and intracellular Ca2+ release for the vasoconstrictor response to Sgd 101/75 (4(2-imidazoline-amino)-2-methyl-indazol-chlorhydrate), an alpha 1-adrenoceptor agonist, was examined in perfused rabbit ear arteries. Sdg 101/75 induced a phasic and a tonic vasoconstrictor response in a concentration-dependent manner. It is a full agonist on the tonic response but a partial agonist on the phasic response. Nifedipine preferentially inhibited the tonic but not the phasic response to Sgd 101/75. Therefore, Sgd 101/75 appears to require both the intracellular Ca2+ release and extracellular Ca2+ influx for its phasic and tonic responses in rabbit ear arteries, respectively.
Wong
P C
PC
DuPont Merck Pharmaceutical Company, Wilmington, DE 19880-0400.
Hart
S D
SD
Timmermans
P B
PB
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001158:Arteries; D002118:Calcium / Q000378:metabolism; D003000:Clonidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004423:Ear / Q000098:blood supply; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology*; D011817:Rabbits; D014661:Vasoconstriction / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D009543:Nifedipine; D003000:Clonidine; C034204:indanidine; D002118:Calcium