骨格筋微小循環における血流調節機構の生体顕微鏡的研究

A microscopic study of the blood flow regulation of the microcirculation in the rabbit tenuissimus muscle

　骨格筋微小循環における血流調節は，交感神経を介する中枢性調節と組織酸素分圧や代謝産物による局所性調節の二つの機構が存在することはよく知られている^1,2）。従来からこれらの調節機構について，その個々の働きについては詳細な解明が行われている。Rosell^3）は生体顕微鏡法を用いて交感神経刺激時の末梢血管を観察した結果，刺激時においては対象とした全ての組織において血管収縮を引き起こすことを報告している。また同様な血管反応は圧受容器反射においても起こることが確認されている^4,5）。

　一方，局所調節因子に関する報告は，骨格筋においては特に組織酸素分圧と毛細血管血流の関係を調べたものが多い^6〜8）。骨格筋毛細血管は組織酸素分圧に対して最も敏感に反応する部位の一つであり，毛細血管開存密度，同赤血球速度等においてその変化が顕微に見られる。

Effects of the local and central blood flow con-trol mechanisms by the tissue Pob₂ and the autonom-ic nervous system on capillary red cell velocity and perfused capillary density were investigated in the rabbit tenuissimus muscle. Microcirculatory re-sponses to the electric stimulation of the carotid si-nus nerve were observed using a microscopic-TV recorder system at the states of different oxygen ten-sion (PO₂) in Tyrode solution suffusing the mus-cle. When PO₂ in the Tyrode solution was eleva-ted, capillary red cell velocity and perfused capil-lary density were decreased both at control and during stimulation but different extents. The rates of relative mean velocity change at control and peak one during stimulation, were -5.5±0.8% and -3.1±1.3% per 10mmHg PO₂ changes, whereas the rates of relative perfused capillary density changes at control and during stimulation were -2.8± 4.0% and -6.2±4.4%. The differences between the changing rates at control and during stimula-tion were both significant for velocity and density (p< 0.01). Regression lines between these changing rates and PO₂ levels revealed that the reflex effect on velocity and density at 20 mmHg was about 1.3 and 4.8 times enhanced at 80 mmHg respectively. These results indicated that resistance change due to the arteriolar smooth muscle contraction elicited by the sympathetic nerve discharge was significantly influenced by the ambient PO₂ level. It was con-cluded that such interaction of local and central blood flow control mechanisms plays an important role for overall regulation of the microcirculation.