Evidence for a direct influence of efferent control upon the mechano-sensitive receptors in the carotid bifurcation.

An efferent control upon the carotid baroreceptor could be achieved by two distinct ways, 1. by influencing the vessel wall mechanics, and 2. by modifying the sensitivity of the receptors. To give evidence that the last mentioned way is really involved, the ganglioglomerular nerve supplying the carotid bifurcation was stimulated with single electrical pulses triggered by the R-wave of the ECG. The time delay between R-wave and electrical stimulus was varied stepwise. Since the baroreflex pathway was kept intact, any changes in the sensitivity of the receptors should result in a blood pressure response. A maximum response was observed by applying the stimulus with a time delay of 45 ms after the R-wave. Because a biological latency has to be added, a gross latency was assumed of about 60 to 80 ms. The systolic pulse in the carotid bifurcation started with a similar time delay after the R-wave of about 65 +/- 3 ms. Therefore the coincidental relationship between increased sensitivity of the receptors caused by stimulation with the systolic pulse was assumed to be the real reason for eliciting the maximum response. The possible importance for the baroreceptor reflex regulation of the circulatory system is discussed.