title: Transient effects of norepinephrine on myocardial oxygen balance.
abstract: In conscious dogs with experimental atrioventricular block and with ventricles paced at constant rate the effects of norepinephrine (NE) and isoproterenol (ISO) on coronary flow, coronary resistance, and myocardial O2-balance were investigated. Myocardial O2-S balance, as estimated from continuous measurement of coronary venous O2-S saturation, was used for the discrimination of coronary dilation induced either directly by vascular beta-adrenoreceptor stimulation or indirectly by increased myocardial metabolism. Following bolus injection of NE (0.3 microgram/kg) or ISO (0.1 microgram/kg) into the pulmonary artery, coronary venous O2-S saturation increased from a control of 25 +/- 2% O2-S saturation (mean +/- S.D.) transiently to 51 +/- 5 and 62 +/- 5% O2-S saturation respectively. After beta1-adrenoreceptor blockade these increases were reduced to 33 +/- 4 and 41 +/- 3% O2-S saturation, respectively. The remaining increase after NE was abolished when atropine was given in addition to beta1-b blockade. After beta1 + 2-adrenoreceptor blockade neither NE nor ISO injection had an effect on coronary venous O2 saturation. After beta1-b blockade was superimposed on ganglionic blockade NE injection led to a decrease in coronary venous O2-S saturation indicating a latent alpha-a activity of NE. NE seems to act directly via beta1-a adrenoreceptors, since no differences were observed in the time courses of changes in coronary venous O2-S saturation after left atrial injection of NE when compared to adenosine. It is concluded that circulating NE like ISO is able to improve myocardial oxygen balance by a direct vasodilating effect on canine coronary vessels mediated by vascular beta1-adrenoreceptors.
mesh_terms: D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D003331:Coronary Vessels / Q000187:drug effects / Q000294:innervation*; D004285:Dogs; D004347:Drug Interactions; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects*; D011433:Propranolol / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects*
chemical_list: D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D011433:Propranolol; D000241:Adenosine; D007545:Isoproterenol; D010100:Oxygen; D009638:Norepinephrine