Dependence on extracellular potassium of the positive inotropic response to St 587, a selective alpha-1 adrenoceptor agonist, in Zucker rat heart ventricle.
The effects of St 587, a selective alpha-1 adrenoceptor agonist, were investigated in non obese and obese Zucker rat heart ventricles. In both groups, the numbers and affinity constants for alpha-1 adrenoceptors were found to be similar. At 4 or 10 mM [K]o, St 587 failed to increase the developed tension whereas at 14 mM [K]o, St 587 significantly increased it in both groups of rats. This effect was reversed by prazosin; St 587 also increased action potential duration at 14 mM [K]o. [K]o is thus important for the occurrence of the inotropic effect of St 587 in 12 week-old Zucker rats, either non obese or obese with reduced beta-adrenoceptor responsiveness. This suggests the participation of phosphoinositide metabolism in the mechanism of St 587 inotropic effect in the rat.
Auclair
M C
MC
Institut de Pharmacologie, Paris, France.
Vernimmen
C
C
Lavau
M
M
Lechat
P
P
D000200:Action Potentials / Q000187:drug effects; D000316:Adrenergic alpha-Agonists; D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D003000:Clonidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006352:Heart Ventricles / Q000503:physiopathology; D009200:Myocardial Contraction / Q000187:drug effects*; D009765:Obesity / Q000503:physiopathology; D010716:Phosphatidylinositols / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*; D011224:Prazosin / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D011924:Rats, Zucker; D013268:Stimulation, Chemical
D000316:Adrenergic alpha-Agonists; D010716:Phosphatidylinositols; C030655:St 587; D003000:Clonidine; D011188:Potassium; D011224:Prazosin