Mechanisms of resetting of arterial baroreceptors: an overview.

Arterial baroreceptors are reset when their afferent nerve activity is reduced at an equivalent arterial pressure and vascular strain. Resetting occurs as a result of stretch of the baroreceptors, usually during an acute or chronic rise in arterial pressure. It may be seen during the diastolic phase of a cardiac cycle (instantaneous resetting), after brief exposure to a sustained elevation of pressure (acute resetting), and after chronic elevation of pressure or in physiologic or pathologic states associated with structural changes in the vascular regions of baroreceptors (chronic resetting). The mechanisms reviewed here include mechanical, ionic and chemical factors. Viscoelastic properties of the carotid sinus and aortic arch may explain the instantaneous resetting that occurs with each cardiac cycle when activity begins in early systole and stops in early diastole. Viscoelastic properties and ionic mechanisms may play a role in acute resetting. Inhibition of Na+K+ ATPase reduces the magnitude of acute resetting. The release of chemicals from the endothelium may modulate baroreceptor activity. Exogenous prostacyclin suppresses and indomethacin augments acute resetting in the rabbit, suggesting that the release of endogenous prostacyclin during a rise in arterial pressure attenuates resetting. Changes in pulsatility and blood flow also may modulate baroreceptor activity. The addition of pulsatile pressure at an increased mean pressure attenuates resetting.(ABSTRACT TRUNCATED AT 250 WORDS)