[Cardiodepressive effects of muscular exercise in spontaneously hypertensive rats]

Conflicting results have been reported on the differences in the cardiovascular reactivity to muscular exercise between normotensive and hypertensive subjects and normotensive subjects with family history of hypertension and normotensive subjects without familial hypertensive history. Also studies performed in spontaneously hypertensive in comparison with normotensive rats have not led to final conclusions. Therefore, the aim of the present study was twofold: to evaluate cardiorespiratory reactivity to different types of muscular exercise in normotensive (WKY) compared to spontaneously hypertensive rats (SHR) at pre-hypertensive and hypertensive stages; to verify the role played by the "muscular reflex drive" in mediating the cardiorespiratory responses in rats. We utilized four groups of anesthetized rats: 8 young WKY, 8 SHR in pre-hypertensive stage, 6 adult WKY and 6 SHR in hypertensive stage. We evaluated the cardiorespiratory responses to (rhythmic) dynamic and (static) isometric contractions of gastrocnemius muscles induced by electrical stimulation of the tibial nerve. Cardiorespiratory responses during the initial phase of dynamic and static contractions of hindlimb muscles were studied. Muscle contractions were elicited by stimulating the tibial nerves at 3 and 100 Hz. We measured: mean arterial pressure (MAP), heart rate (HR), and pulmonary ventilation (VE). Both types of exercise caused a significant decrease in MAP and a significant increase in VE while HR did not change significantly. The four groups of rats did not show significant differences in the pattern of cardiorespiratory responses to muscular exercise. The cardiorespiratory reflexes initiated by activation of muscle receptors, verified by interrupting the afferents from the contracting muscles.(ABSTRACT TRUNCATED AT 250 WORDS)