Phase resetting of arterial vasomotion by burst stimulation of perivascular nerves

Arteries display cyclic diameter variations, vasomotion. In vivo, these rhythmic contractions are modulated by the influence of sympathetic nerves. In this study, we investigated the effect of burst stimulation of intramural nerves in vitro on the vasomotion of rat mesenteric small arteries. Vessels were mounted for isometric force measurement. After initiation of vasomotion with noradrenaline (0.5-2 microM), periarterial sympathetic nerves were stimulated electrically (10 impulses at 20 Hz) at approximately half-minute intervals. With a delay of 2-3 s, a neurogenic burst caused a brief contraction of the vascular smooth muscle and altered the period of the current vasomotion cycle. The effect on amplitude decayed rapidly and was practically not apparent in the next vasomotion cycle after the burst. With respect to period, stimulation at increasing intervals from the trough in force of vasomotion caused gradual prolongation of the cycle until a critical interval was reached, after which cycle duration was reduced instead. Since subsequent cycles were not affected, a change in phase remained. When two segments of oscillating arteries were mounted in a two-vessel myograph, simultaneously applied bursts of impulses synchronized their oscillation. The data suggest that changes in neural activity are able to make different vessels oscillate in phase, thereby coordinating vasomotion in different parts of the vascular tree, possibly explaining the synchronicity of vasomotion in different vascular beds that can be observed in vivo.