Abstract
Hypertensive patients present an exaggerated increase in blood pressure and elevated cardiovascular risk during exercise. Although controversial, human studies suggest that group III and IV skeletal muscle afferents might have a contribution to this abnormal response. Here, we evaluated whether attenuation of the group III and IV muscle afferent signal of hypertensive men eliminates the exaggerated increase in blood pressure during exercise. Eight hypertensive men performed two sessions of 5-min cycling exercise at 40 W. Between sessions, the subjects were provided with lumbar intrathecal injection of fentanyl, a μ-opioid receptor agonist, to attenuate the central projection of opioid-sensitive group III and IV muscle afferent nerves. The cardiovascular response to exercise of these subjects was compared to that of six normotensive men. During cycling, the hypertensive group demonstrated an exaggerated increase in blood pressure compared to the normotensive group (+17 ± 3 vs. +8 ± 1 mmHg, respectively; P < 0.05), while the increase in heart rate, stroke volume, cardiac output, and vascular conductance was similar (P > 0.05). Fentanyl inhibited blood pressure response to exercise in the hypertensive group (+11 ± 2 mmHg) to a level comparable to that of the normotensive group (P > 0.05). Moreover, fentanyl increased the responses of vascular conductance and stroke volume to exercise (P < 0.05), while heart rate response was attenuated (P < 0.05) and cardiac output response was maintained (P > 0.05). This study shows that attenuation of the exercise pressor reflex normalizes blood pressure response to cycling exercise in hypertensive individuals.
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