Microcirculatory responses to carotid sinus nerve stimulation at various ambient O₂ tension in the rabbit tenuissimus muscle

To quantify the integrated effects of local and central control mechanisms through tissue metabolites and the autonomic nervous system on the peripheral vascular beds, microcirculatory responses to the carotid sinus nerve stimulation at various levels of ambient oxygen tension (PO₂) were measured in the rabbit tenuissimus muscle suffused with oxygenated Tyrode solution, using a microscope-TV system. The statistical analysis of the experimental data exhibited that both capillary red cell velocity and perfused capillary density at the control state were significantly decreased as PO₂ was elevated (P < 0.01) and that the stimulation also significantly augmented their values (P < 0.01) except for the peak velocity data. Regression analysis indicated that both the velocity and density responses to PO₂ changes during stimulation were less sensitive than those at the control state. For instance, the vasodilating effect of stimulation on density at PO₂ mm Hg was enhanced by about four-fold at 80 mm Hg, although the effect on velocity was increased only by 16% with the same PO₂ change. From these results, it was concluded that the microcirculatory changes due to the arteriolar smooth muscle contraction evoked by unit sympathetic discharge was significantly influenced by the ambient PO₂ level. Such synergistic interaction of the local and central control mechanisms like a series-coupled gain control system was suspected to play an important role in the overall regulation of the microcirculation.