Interrelation Between Central and Peripheral Mechanisms Regulating Blood Pressure

Electrical stimulation of selected discrete sites in the diencephalon induced a profound and coordinated response consisting of increased respiratory activity, limb movements, and cardiovascular adjustments. The effects on the cardiovascular system were similar to those of exercise, although the increases in aortic pressure, left ventricular pressure, and heart rate were greater. Massive splanchnicnerve discharge occurred immediately when the diencephalon was stimulated, but splanchilic activity abruptly fell below control levels with cessation of the stimulus. The increase in respiratory activity and the organized running movements seen during stimu lation apparently did miot contribute to the pressor and cardioaccelerator responses. There appeared to be no marked difference between control and diencephalic-stimulation experiments in the ease with which in duced pressure pulsations in the partially isolated carotid sinus caused bradycardia and blood-pressure depression. It may be that the influences of the diencephalon and carotid- sinus reflex upon blood pressures are inde pendent and sum algebraically. Experiments in which effects of epinephrine on splanchnic-nerve activity and systemic arterial pressure were measured before and during dieneephalic stimulation did not support the concept that catecholamines have an important role in normal pressor responses.