Exercise induced changes of catecholamines and potassium in plasma of dogs after treatment with propranolol.
Previous studies in man have shown that during beta-adrenoceptor blockade physical exercise caused a significantly greater elevation of plasma catecholamines than without blockade. After blockade of beta-adrenoceptors, increased levels of circulating catecholamines should have an unopposed effect on adrenergic alpha-receptors. In order to elucidate such an effect, experiments were performed with 7 trained dogs before and after acute beta-adrenoceptor blockade (0.1 mg/kg (-)-propranolol i. v.). Exercise was performed on a conveyor (10 min, 10 km/h, slope 10%). Besides catecholamine concentrations in plasma, as an index of alpha-receptor-stimulation potassium concentrations in plasma were determined. Immediately after exercise, plasma noradrenaline was increased from 310 to 579 pg/ml, plasma adrenaline from 136 to 222 pg/ml and plasma potassium from 4.23 to 4.6 mmol/l. After beta-adrenoceptor blockade exercise caused a significantly higher increase in plasma noradrenaline from 352 to 755 pg/ml and plasma adrenaline from 172 to 260 pg/ml. Also plasma potassium concentrations were significantly elevated from 4.03 to 5.05 mmol/l. The results indicate an enhanced reflex activation of sympatho-neuronal and sympatho-adrenal mechanisms during exercise after beta-adrenoceptor blockade; the increased concentrations of noradrenaline at the adrenoceptors might reduce the efficiency of beta-blockade. Concomitantly, increased stimulation of alpha-adrenoceptors is elicited, which becomes obvious by an increase of potassium concentration in plasma.
D000818:Animals; D002395:Catecholamines / Q000097:blood*; D004285:Dogs; D004837:Epinephrine / Q000097:blood; D006339:Heart Rate / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000097:blood; D005082:Physical Exertion; D011188:Potassium / Q000097:blood*; D011433:Propranolol / Q000494:pharmacology*
D002395:Catecholamines; D011433:Propranolol; D007545:Isoproterenol; D011188:Potassium; D009638:Norepinephrine; D004837:Epinephrine