[Effect of hypothalamic stimulation on RMBF and SP content in IML of spinal cord in rabbits]

Experiments were performed on 48 urethane-chloralose anaesthetized, gallamine triethiodide immobilized and vagotomized rabbits under artificial ventilation. Radiolabeled microspheres were injected into the left atrium during stimulation of the left or right dorsomedial hypothalamic nucleus (LDMH or RDMH) to measure regional myocardial blood flow (RMBF). RDMH stimulation produced relatively little flow reduction of the left ventricle, whereas LDMH stimulation produced an obvious flow reduction. No significant change occurred in the right ventricle. Meanwhile, LDMH or RDMH stimulation caused increases of mean arterial blood pressure (MABP) and changes of epicardial electrogram (EECG) ST segment, but no significant changes in heart rate. EECG ST segment was elevated in relation to the reduction of RMBF in left ventricle (r = -0.825, P less than 0.001). Linear regression analysis of MABP change in relation to left ventricle RMBF showed no significant correlation. In intact rabbits, it was demonstrated that DMH stimulation caused an decrease of substance P (SP) immunoreactive material in bilateral intermediolateral cell columns (IML) of T2-5 spinal cord concomitantly with an elevation in MABP and EECG ST changes. The results suggest that electrical stimulation of DMH can elicit coronary constriction, decrease in RMBF, elevation of EECG ST segment and increase in MABP, which may be mediated by the release of SP immunoreactive material in the IML of the spinal cord.