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Department of Physiology, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272
The influence of daily spontaneous running
(DSR) on the sympathetic (SC) and parasympathetic components of the
arterial baroreflex control of heart rate (HR) was examined in 16 female Long Evans rats [8 sedentary (SED) and 8 DSR]. After
8-9 wk of SED control or DSR, animals were chronically
instrumented with arterial and venous catheters. DSR resulted in an
increased heart weight-to-body weight ratio (2.71 ± 0.11 vs. 3.09 ± 0.09 g/kg) and a resting bradycardia (378 ± 6 vs. 330 ± 5 beats/min). Arterial baroreflex function was examined during ramp
infusions of phenylephrine and sodium nitroprusside under the following
three experimental conditions: 1)
control, 2) after
1-adrenergic receptor blockade
(1-X), and 3) after muscarinic-cholinergic
receptor blockade (M-X). Arterial baroreflex function parameters were
compared between SED and DSR rats. In the control condition, DSR
attenuated the range (182 ± 15 vs. 124 ± 18 beats/min), maximum
HR (464 ± 9 vs. 394 ± 15 beats/min), and maximal gain
(Gmax; 5.57 ± 0.42 vs. 3.2 ± 0.45 beats · min
1 · mmHg1).
Similarly, after M-X, DSR attenuated the range (84 ± 5 vs. 62 ± 8 beats/min), maximum HR (449 ± 11 vs. 412 ± 11 beats/min), and
Gmax (2.73 ± 0.37 vs. 1.57 ± 0.32 beats · min1 · mmHg1).
In contrast, after 1-X, DSR did
not alter the range (61 ± 13 vs. 70 ± 7 beats/min), maximum HR
(326 ± 9 vs. 313 ± 7 beats/min), or
Gmax (3.04 ± 0.54 vs. 3.75 ± 0.52 beats · min1 · mmHg1).
Results demonstrate that DSR attenuated the arterial baroreflex control
of HR by reducing the SC.
autonomic nervous system
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