Cardiac afferents attenuate the muscle metaboreflex in the rat.
The influence of cardiac afferents on the muscle metaboreflex was examined in 16 rats instrumented with a Silastic-tipped catheter in the pericardial space and right atrium, Doppler ultrasonic flow probe and a pneumatic vascular occluder around the terminal aorta, and a Teflon catheter in the thoracic aorta. In protocol I (cardiac efferent and afferent blockade), the muscle metaboreflex was examined under three experimental conditions: 1) control, 2) cardiac autonomic efferent blockade [intrapericardial methylscopolamine (10 micrograms/kg) and propranolol (50 micrograms/kg)], and 3) combined cardiac autonomic efferent and afferent blockade (intrapericardial procainamide, 2%). In protocol II (blood volume expansion), the muscle metaboreflex was examined before and after 15% blood volume expansion. Mild treadmill exercise (9 m/min, 10% grade) increased heart rate (71 +/- 9.4 beats/min), mean arterial pressure (12 +/- 2.0 mmHg), and terminal aortic blood flow velocity (6 +/- 1.0 kHz). During exercise, a reduction of terminal aortic blood flow velocity (10.5 +/- 1.1%) reduced mixed venous PO2 18 +/- 6%. The gain of the muscle metaboreflex in the control condition was 14.6 +/- 2.9 mmHg/kHz. Efferent blockade reduced the gain 51 +/- 7%. However, combined cardiac efferent and afferent blockade increased the gain 207 +/- 64% above the efferent blocked condition and restored the gain to levels above those obtained in the control condition (18.3 +/- 4.6 mmHg/kHz). In addition, 15% blood volume expansion reduced the gain of the muscle metaboreflex regulation of mean arterial pressure and heart rate (44 +/- 9.5% and 41 +/- 12.0%, respectively). Thus cardiac afferents tonically inhibit the pressor response to a reduction in terminal aortic blood flow velocity during exercise.
Department of Physiology, Northeastern Ohio Universities College of Medicine, Rootstown 44272.
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Collins
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DiCarlo
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001810:Blood Volume / Q000187:drug effects / Q000502:physiology; D006321:Heart / Q000187:drug effects / Q000294:innervation* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D019832:N-Methylscopolamine; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D010276:Parasympatholytics / Q000494:pharmacology; D005082:Physical Exertion / Q000502:physiology; D011342:Procainamide / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012602:Scopolamine Derivatives / Q000494:pharmacology; D013048:Specimen Handling
D010276:Parasympatholytics; D012602:Scopolamine Derivatives; D011433:Propranolol; D011342:Procainamide; D019832:N-Methylscopolamine