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Direct coupling between blood flow and metabolism at the capillary level in striated muscle
B R Berg1, K D Cohen, I H Sarelius
1Department of Pharmacology and Physiology, School of Medicine and Dentistry, University of Rochester, New York 14642, USA.
Insights
Muscle fiber stimulation increases capillary blood flow through conducted vasodilation. This response, mediated by local metabolic signals, enhances blood supply to active muscle regions.
Area of Science:
- Physiology
- Microcirculation
- Muscle Metabolism
Background:
- Capillary networks in hamster cremaster muscle exhibit modular organization.
- Understanding local blood flow regulation is crucial for muscle metabolism studies.
Purpose of the Study:
- To investigate the local coupling between muscle contraction and capillary blood flow.
- To identify the mechanisms responsible for changes in capillary flow during muscle activity.
Main Methods:
- Stimulation of muscle fibers underlying specific capillary modules using micropipettes.
- Measurement of capillary erythrocyte flow, content, and velocity.
- Analysis of arteriolar dilation in response to muscle fiber stimulation.
- Pharmacological and osmotic challenges to elucidate signaling pathways.
Main Results:
- Muscle fiber stimulation significantly increased capillary erythrocyte flow.
- Increased flow was due to elevated erythrocyte content and velocity at different frequencies.
- Active muscle contraction, not mechanical tugging, triggered the flow increase.
- Upstream arterioles dilated, with greater dilation at higher stimulation frequencies.
- Conducted vasodilation was observed, affecting upstream arterioles.
- Sucrose abolished vasodilation, while tetrodotoxin had no effect.
Conclusions:
- Local coupling between capillary flow and muscle contraction involves conducted vasodilation.
- This vasodilation mechanism enhances blood supply to active muscle.
- The response appears to be mediated by metabolic signals rather than neural input.
Abstract:
In hamster cremaster muscle, capillary networks consist of anatomically invariant subunits termed modules [Berg, B. R., and I. H. Sarelius, Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H1215-H1222, 1995]. To explore local coupling between blood flow and metabolism, we used micropipettes to stimulate five to six muscle fibers running underneath specified capillary modules. Capillary erythrocyte flow increased significantly at all stimulation frequencies because of increased erythrocyte content at 2 Hz and increased erythrocyte velocity at 4 and 8 Hz. Erythrocyte flow did not increase when the fibers underlying the module were mechanically tugged but did not actively contract at these frequencies. Increased capillary flow was accommodated by dilation of three upstream arteriolar generations: the module inflow arteriole dilated significantly at all frequencies, and further upstream, dilations were significant at higher frequencies. Other module inflow arterioles in the same capillary network as the stimulated module did not dilate. Dilations in the module inflow arteriole were abolished by 600 mosM sucrose but were unaffected by 10(-6) M tetrodotoxin. These data suggest that local coupling between capillary flow and muscle contraction includes a conducted vasodilation that is responsible for the remote upstream dilations.