Angiotensin peptides and baroreflex control of sympathetic outflow: Pathways and mechanisms of the medulla oblongata

The baroreceptor reflex is a relatively high gain control system that maint ains arterial pressure within normal limits. To a large extent, this is acc omplished through central neural pathways responsible for autonomic outflow residing in the medulla oblongata. The circulating renin-angiotensin syste m also contributes to the regulation of blood pressure, predominantly throu gh its effects on the control of hydromineral balance and fluid volume. All the components of the renin-angiotensin system are also found in the brain . One of the principal products of the renin-angiotensin system cascade (br ain or blood), angiotensin II, modulates the baroreceptor reflex by diminis hing the sensitivity of the reflex and shifting the operating point for reg ulation of sympathetic outflow to higher blood pressures. This paper review s our current knowledge about the neuronal pathways in the medulla oblongat a through which angiotensin peptides alter the baroreceptor reflex control of sympathetic nerve activity. Emphasis is placed on the probable component s and neural mechanisms of the medullary baroreflex are that account for th e ability of angiotensin peptides to change the sensitivity of the barorece ptor reflex and to shift the baroreceptor reflex control of sympathetic out flow to higher blood pressures in a pressure-independent manner. (C) 2000 E lsevier Science Inc.