Blood flow to different rat skeletal muscle fiber type sections during isometric contractions in situ

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Abstract
TERJUNG, R. L. and B. M. ENGBRETSON. Blood How to different rat skeletal muscle fiber type sections during isometric contractions in situ. Med. Sci. Sports Exerc, Vol. 20, No. 5 (Supplement), pp. S124-S130, 1988. In whole skeletal muscle, peak blood flow is known to correlate with the capacity for oxidative metabolism. Since most mammalian skeletal muscle is comprised of different fiber types whose oxidative potential varies widely, the possibility of heterogeneous blood flow distribution within a given muscle was investigated. An in situ preparation of the rat gastrocnemius-soleus-plantaris muscle group was used and blood flow measured by the radiolabeled microsphere technique. Blood flow at rest averaged 5-6 ml·min-1·100 g-1 in fast-twitch white (FTW) fiber sections, while flows to fasttwitch red (FTR) and slow-twitch red (STR) muscle were 10-12 ml·min-1·100 g-1. Isometric twitch contractions generated large (12-15 times above rest) increases in blood flow to all fiber type sections that tended to decrease at higher frequencies. Tetanic contractions result in greater tension development and higher blood flows in the red fiber sections. The highest blood flow to the FTR section was 300 ml·min-1·100 g-1 a value 3-4-fold greater than the maximum for the FTW fiber section. Peak blood flow to the STR (soleus) was intermediate between the two fast fiber types. Differences in blood flow response between fiber sections could not be dismissed due to measurement artifact. Thus, the capacity for blood flow is fairly proportional to the differences in oxidative capacity among fiber types. Blood flow to the skeletal muscle fiber types of the rat also differed qualitively in response to contractions. During low frequency stimulation conditions, blood flows to the red fiber sections were initially in excess of that required to sustain contractions but subsequently diminished with time to values more closely reflecting energy demands. This time dependent relative hyperemia was not found in FTW muscle.

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