Inversion of cardiac inotropism response to carotid arteries occlusion in dogs treated with propranolol.
The effect of beta-adrenergic blockade achieved by propranolol (0.5-1.0 mg/kg) on the inotropic alterations induced by adrenergic hyperactivity resulting from bilateral carotid occlusion (BCO) was analysed in 25 dogs anesthetized with morphine (2 mg/kg) and sodium pentobarbital (20 mg/kg). The heart rate was kept unchanged by means of a pace-maker. The first derivative of ventricular pressure (dp/dt) was considered as contractility index. Because BCO is followed by increase of left ventricle end-diastolic pressure (LVEDP) and of blood pressure (BP), to avoid the influence of these variables on dp/dt, we have reduced preload and afterload by means of hemorrhage (group A) and alpha-adrenergic blocker administration--phentolamine (group B). The carotid occlusion promoted similar variations in hemodynamic parameters in the two groups--there was a significant increase of blood pressure and LVEDP. BCO did not produce alteration in dp/dt values in both groups; when BP and LVEDP in group A were reduced, there was a significant reduction of dp/dt (2 927 +/- 139 to 2 066 +/- 95 mmHg/s; p less than 0.01). However there was no dp/dt alteration in group B (2 559 +/- 239 to 2 512 +/- 285 mmHg/s). These results suggest that during increase of sympathetic activity, anesthetized dogs under beta-adrenergic blockade show contractility depression. This could be related to secondary myocardic hypoxia and coronary vasoconstriction due to coronary alpha-adrenergic hyperactivity, once cardiac inotropism response can be alleviated by alpha-adrenergic blockers.
D000818:Animals; D001794:Blood Pressure; D002339:Carotid Arteries / Q000502:physiology*; D003864:Depression, Chemical; D004285:Dogs; D006339:Heart Rate; D006439:Hemodynamics; D006470:Hemorrhage / Q000503:physiopathology; D008297:Male; D009200:Myocardial Contraction; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology*
D011433:Propranolol; D010646:Phentolamine