Exaggerated pressor and sympathetic responses to stimulation of the mesencephalic locomotor region and exercise pressor reflex in type 2 diabetic rats

The cardiovascular responses to exercise are potentiated in patients with type 2 diabetes mellitus (T2DM). However, the underlying mechanisms causing this abnormality remain unknown. Central command (CC) and the exercise pressor reflex (EPR) are known to contribute significantly to cardiovascular control during exercise. Thus these neural signals are viable candidates for the generation of the abnormal circulatory regulation in this disease. We hypothesized that augmentations in CC as well as EPR function contribute to the heightened cardiovascular responses during exercise in T2DM. To test this hypothesis, changes in mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) in response to electrical stimulation of mesencephalic locomotor region (MLR), a putative component of the central command pathway, and activation of the EPR, evoked by electrically induced hindlimb muscle contraction, were examined in decerebrate animals. Sprague-Dawley rats were given either a normal diet (control) or a high-fat diet (14-16 wk) in combination with two low doses (35 mg/kg week 1, 25 mg/kg week 2) of streptozotocin (T2DM). The changes in MAP and RSNA responses to MLR stimulation were significantly greater in 'T2DM compared with control (2.739 +/- 123 vs. 1.298 +/- 371 mmHg/s, 6,326 +/- 1,621 vs. 1,390 +/- 277%/s, respectively, P < 0.05). Similarly. pressor and sympathetic responses to activation of the EPR in diabetic animals were significantly augmented compared with control animals (436 +/- 74 vs. 134 +/- 44 mmHg/s, 645 +/- 135 vs. 139 +/- 65%/s. respectively. P < 0.05). These findings provide the first evidence that CC and the EPR may generate the exaggerated rise in sympathetic activity and blood pressure during exercise in T2DM.