Arteriolar vasomotion and arterial pressure reduction in rabbit tenuissimus muscle.

Spontaneous arteriolar vasomotion and its relation to arterial pressure reduction was studied in the rabbit tenuissimus muscle using intravital microscopy. Vasomotion was observed in all transverse arterioles and their first-order side branches. Vasomotion frequency ranged from 5 to 32 cycles per minute (median: 25 cpm). The relative vasomotion amplitude in transverse arterioles varied from 0.06 to 0.44 (median: 0.22). Vasomotion was generally of the on-off type in first-order side branches. A gradual reduction in arterial pressure as achieved by aortic occlusion resulted in an abrupt disappearance of vasomotion. Vasomotion disappeared between 19 and 59 mm Hg (median: 30.4 mm Hg). No differences were found between the pressures at which vasomotion ceased in transverse arterioles and first-order side branches. With a further reduction of arterial pressure transverse arterioles attained a maximal diameter of 98-265% (median: 119%) of the maximal diameter during vasomotion. After release of occlusion vasomotion reappeared much earlier in the first-order side branches than in their feeding transverse arterioles. It is concluded that although vasomotion influences capillary perfusion, it does not play a major role in the adaptation of vascular resistance following a reduction in arterial pressure.