The differential effects of alpha 2-adrenergic stimulation on the myocardium and coronary vessels in the isolated rat heart.
The differential effects of alpha 2-adrenoceptor stimulation on myocardial contractility and coronary circulation were examined in the isolated perfused rat heart. We studied 20 Sprague-Dawley rats of similar age (26-28 weeks) and body weight (500-550 gm). Myocardial contractility (LV +dp/dt and developed pressure, LVP) and coronary flow resistance (CFR) were tested in the isolated isovolumic hearts using Langendorff preparation at a constant perfusion rate (2.5 ml/min/100 g BW) of Krebs-Henseleit bicarbonate solution. Group I (N-7) received B-HT 920 (specific alpha 2-adrenergic agonist, 0.6 to 58 micrograms/min), Group II (N-7) received B-HT 920+Yohimbine (300 nM in the perfusate). Group III (N-6) received vehicle only. Baseline LVP, LV +dP/dt and CFR were not significantly different among the 3 groups. During drug or vehicle administration, LVP and LV +dP/dt remained unchanged in all the groups. Coronary flow resistance increased in a dose-response fashion with a maximum increase of 22.7 +/- 3.6 (SE) mmHg/ml/min/g LV in Group I, and 10.5 +/- 2.0 mmHg/ml/min/g LV in Group II (p less than 0.02). We conclude that in the Sprague-Dawley rat heart, the physiologic effects of alpha 2-adrenoceptors are predominant in the coronary circulation but not in the myocardium itself possibly because of absence of post-synaptic alpha 2-adrenergic receptors in the rat myocardium.
Hirakata
H
H
Department of Heart and Hypertension Research, Cleveland Clinic Foundation, Ohio.
Fouad-Tarazi
F M
FM
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001381:Azepines / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D003326:Coronary Circulation / Q000187:drug effects; D003331:Coronary Vessels / Q000187:drug effects / Q000502:physiology*; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D014655:Vascular Resistance / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; C024763:talipexole; D007545:Isoproterenol