Activation of peripheral chemoreceptors causes positive inotropic effects in a working heart-brainstem preparation of the rat.
1. The aim of the present study was to evaluate the effects of peripheral chemoreceptor activation on myocardial contractility in an anaesthetic-free decerebrated rat preparation. 2. In the decerebrated and retrogradely perfused working heart-brainstem preparation, we recorded phrenic nerve activity, left ventricular (LV) pressure (microtip Millar catheter), LV dP/dT, heart rate and aortic perfusion pressure before and after activating peripheral chemoreceptors with bolus intra-arterial injections of KCN. 3. Without cardiac pacing, chemoreflex activation caused falls in heart rate (-108 +/- 21 b.p.m.) and complex polyphasic changes in LV pressure and LV dP/dT. If the heart was paced, chemoreflex activation caused significant rises in LP pressure (+16 +/- 3 mmHg) and LV dP/dt (+778 +/- 93 mmHg/s). These positive inotropic effects were significantly and substantially attenuated by beta-adrenoceptor blockade with atenolol. In all instances, chemoreflex activation elicited potent tachypnoeic responses. 4. In conclusion, activation of peripheral chemoreceptors in non-anaesthetized rats evokes a positive inotropic response that is sympathetically mediated. This observation may be relevant for the evaluation of neurally induced effects of acute hypoxia on the ventricular myocardium.
Braga
Valdir A
VA
Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil.
Zoccal
Daniel B
DB
Soriano
Renato N
RN
Antunes
Vagner R
VR
Paton
Julian F
JF
Machado
Benedito H
BH
Nalivaiko
Eugene
E
D058671:Adrenergic beta-1 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001262:Atenolol / Q000494:pharmacology; D001794:Blood Pressure; D001933:Brain Stem / Q000187:drug effects / Q000502:physiology*; D002304:Cardiac Pacing, Artificial; D002316:Cardiotonic Agents / Q000494:pharmacology; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000378:metabolism*; D003655:Decerebrate State; D006321:Heart / Q000187:drug effects / Q000294:innervation*; D006339:Heart Rate; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D010477:Perfusion; D010791:Phrenic Nerve / Q000502:physiology; D011190:Potassium Cyanide / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism; D012018:Reflex / Q000187:drug effects; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D016277:Ventricular Function, Left / Q000187:drug effects; D017725:Ventricular Pressure
D058671:Adrenergic beta-1 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D002316:Cardiotonic Agents; D018342:Receptors, Adrenergic, beta-1; D001262:Atenolol; D011190:Potassium Cyanide