Interactive effects of K+, acidosis, and catecholamines on isolated rabbit heart: implications for exercise.
Intense exercise can double arterial K+ concentration, decrease pH by 0.4 units, and increase catecholamines 15-fold. Any one of these changes may be cardiotoxic in a subject at rest, yet these changes are well tolerated in exercise. We tested the interactive effects of extracellular K+ concentration ([K+]o), metabolic acidosis (pH 7.0), and raised catecholamines in the isolated working rabbit heart when they were changed with similar kinetics and concentrations to those seen in exercise. Raised [K+]o (8 and 12 mM) significantly decreased aortic flow (AF) by 23 and 76%, respectively (P < 0.01). Acidosis decreased AF by 19% (P < 0.05) and by 38% in combination with 8 mM [K+]o (P < 0.05), making their combined effect additive. Either epinephrine (80 nM), norepinephrine (80 nM) or extracellular Ca2+ concentration (5 mM) offset the negative effects of 8 and 12 mM [K+]o on AF. Norepinephrine also improved AF in 8 mM [K+]o with acidosis. Thus, there may be a beneficial interaction among changes in K+, catecholamines, and acidosis during exercise such that each could offset the others' potentially harmful effects.
Leitch
S P
SP
University Laboratory of Physiology, Oxford, United Kingdom.
Patterson
D J
DJ
D000138:Acidosis / Q000378:metabolism* / Q000503:physiopathology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002302:Cardiac Output; D002304:Cardiac Pacing, Artificial; D002395:Catecholamines / Q000096:biosynthesis*; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits
D002395:Catecholamines; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine