Total Systemic Autoregulation in the Dog and Its Inhibition by Baroreceptor Reflexes

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Abstract
Although many organs maintain constant blood flow despite changes in perfusion pressure, autoregulation in the total systemic circulation has only been reported in animals after destruction of the central nervous system. The present study examined the role of the baroreceptors in this autoregulatory response in open-chest dogs anesthetized with chloralose-urethane. Cardiac output was varied over nearly a twofold range by altering myocardial contractility with either inotropic agents or controlled myocardial ischemia. Cardiac output, determined by dye dilution, and mean aortic pressure stabilized within 3 minutes after the start of infusions of calcium (15-62 mg/min) into the cannulated left coronary artery or the reduction of coronary flow. With bilateral vagotomy and carotid sinus denervation, autoregulation of total peripheral flow was observed. Thus, changes in cardiac output evoked parallel changes in total peripheral resistance and wide variations in aortic pressure. However, with the baroreceptors intact, changes in cardiac output evoked inverse changes in total peripheral resistance which resulted in regulation of aortic pressure. We concluded that autoregulation in peripheral vascular beds could result in autoregulation of total peripheral flow after simple baroreceptor denervation. However, the baroreceptor reflexes normally achieved regulation of aortic pressure by inhibiting autoregulation in much of the peripheral circulation.