Attenuation of postexertional hypotension by cardiac afferent blockade.
*Heart Arrest; *Physical Exertion; Afferent Pathways/physiology; Animals; Blood Pressure/drug effects; Efferent Pathways/physiology; Heart Rate/drug effects; Hypotension/*physiopathology; Inbred SHR; Induced; Pressoreceptors/drug effects; Procainamide/pharmacology; Rats; Reference Values
Naloxone eliminates postexertional hypotension (PEH) in human and animal models. The effect of naloxone on sympathetic activity during hemorrhage and generation of arterial baroreflex function curves can be stimulated by blockade of cardiac afferent receptors. We tested the hypothesis that cardiac afferent blockade would eliminate PEH in eight spontaneously hypertensive rats (SHR). Rats were instrumented with a Silastic-tipped catheter inserted into the pericardial space. Four weeks later, a Teflon catheter was placed in the descending aorta via the left common carotid artery for measurement of mean arterial pressure (MAP) and heart rate (HR). MAP and HR were examined before (preexercise) and after (postexercise) a single bout of dynamic treadmill exercise (9-12.0 m/min, 10-18% grade for 30-40 min) under three experimental conditions: control, cardiac efferent blockade, and combined cardiac efferent and afferent blockade. MAP significantly decreased (29 +/- 5 and 25.6 +/- 4 mmHg) in the control and cardiac efferent blockade conditions after exercise. However, when cardiac afferents were blocked, the hypotensive response to mild dynamic exercise was significantly attenuated (-6 +/- 3 mmHg). Thus blockade of cardiac afferents eliminated PEH in the SHR. These data suggest that inhibitory influence of cardiac afferents on the circulation may be enhanced after exercise.
Collins H L; DiCarlo S E
The American journal of physiology
1993
1993-10
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1152/ajpheart.1993.265.4.H1179" target="_blank" rel="noreferrer noopener">10.1152/ajpheart.1993.265.4.H1179</a>
Cardiac afferents attenuate the muscle metaboreflex in the rat.
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
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.
Collins H L; DiCarlo S E
Journal of applied physiology (Bethesda, Md. : 1985)
1993
1993-07
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1152/jappl.1993.75.1.114" target="_blank" rel="noreferrer noopener">10.1152/jappl.1993.75.1.114</a>