EFFECT OF LIMB ISCHAEMIA ON BLOOD PRESSURE AND THE BLOOD PRESSURE‐HEART RATE REFLEX IN THE RAT

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Abstract
The effects of bilateral hind-limb ischemia on blood pressure and on the blood pressure-heart rate reflex were studied in the rat. Limb ischemia increased blood pressure and decreased the elevation and slope of the regression line describing the relationship between heart period (H.P.) and mean arterial pressure (M.A.P.). Nociceptive afferents from muscle receptors using long fiber tracts in the anterolateral part of the spinal cord seem to be responsible for the changes seen. The changes in the blood pressure-heart rate reflex were mediated by a combination of vagal inhibition and sympathetic activation. The efferent pathway for the pressor effect was in the sympathetic outflow. Central catecholaminergic neurons were involved in the pressor effect of limb ischemia but not in the changes in the blood pressure-heart rate reflex. Electrolytic lesions in the posterior hypothalamus attenuated the inhibition of the reflex and neurons in the defense area may be activated by limb ischemia. The interaction between limb ischemia and the H.P.-M.A.P. relationship was not affected by opioid antagonists. After the period of ischemia there was an increase in the elevation of the regression line describing the relationship between H.P. and M.A.P. which was secondary to the fall in body temperature characteristic of this phase of the response to injury.