Cardiac afferents attenuate the muscle metaboreflex in the rat.

Cardiac afferents attenuate the muscle metaboreflex in the rat.

Collins H L; DiCarlo S E

Journal of applied physiology (Bethesda, Md. : 1985)

1993

1993-07

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.

Afferent/drug effects/*physiology; Animals; Aorta/drug effects/physiology; Blood Pressure/drug effects/physiology; Blood Volume/drug effects/physiology; Heart Rate/drug effects/physiology; Heart/drug effects/*innervation/physiology; Muscles/drug effects/*metabolism; N-Methylscopolamine; Neurons; Parasympatholytics/pharmacology; Physical Exertion/physiology; Procainamide/pharmacology; Propranolol/pharmacology; Rats; Reflex/drug effects/*physiology; Scopolamine Derivatives/pharmacology; Specimen Handling

Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).

114–120

1

75