Electrically Induced Static Exercise Elicits a Pressor Response in the Decerebrate Rat

1. The purpose of this investigation was to determine if activation of the exercise pressor reflex in the decerebrate rat induced circulatory responses comparable to those reported in large mammalian species. 2. To activate both mechanically and metabolically sensitive afferent fibres, static hindlimb contractions were induced by stimulating the cut ends of L4 and L5 spinal ventral roots in Sprague-Dawley rats (300-400 g). To selectively stimulate mechanically sensitive receptors, hindlimb muscles were passively stretched. 3. In intact halothane-anaesthetized animals (n = 10), static contraction and passive stretch induced a decrease in mean arterial pressure (Delta MAP = -17 +/- 3 and -8 +/- 1 mmHg for contraction and stretch, respectively) and heart rate (HR). In contrast, MAP increased 23 +/- 2 mmHg during contraction and 19 +/- 3 mmHg during stretch in decerebrate rats (n = 10). These pressor responses were accompanied by a significant tachycardia. In decerebrate animals, the reintroduction of halothane attenuated the increase in MAP and HR caused by both contraction and stretch. 4. In both anaesthetized and decerebrate rats, sectioning the spinal dorsal roots innervating the activated skeletal muscle eliminated responses to contraction and stretch. This finding indicated that an intramuscular neural reflex mediated the response to each stimulus. 5. The results demonstrate that a decerebrate preparation in the rat is a reliable model for the study of the exercise pressor reflex. Development of the model would enable the study of this reflex in a variety of pathological conditions and allow investigation of the mechanisms controlling cardiovascular responses to exercise in health and disease.