Rapid biphasic arteriolar dilations induced by skeletal muscle contraction are dependent on stimulation characteristics

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Abstract
To test the hypothesis that measurable changes in microvasculature dilation occur in response to a single short-duration tetanic contraction, we contracted three to five skeletal muscle fibres of the hamster cremaster muscle microvascular preparation (in situ) and evaluated the response of an arteriole overlapping the active muscle fibres. Arteriolar diameter (baseline diameter = 16.4 ± 0.9 µm, maximum diameter = 34.7 ± 1.2 µm) was measured before and after a single contraction resulting from a range of stimulus frequencies (4, 10, 20, 30, 40, 60, and 80 Hz) within a 250- or 500-ms train. Four and 10 Hz produced a significant dilation at 2.9 ± 0.4 and 6.5 ± 2.8 s, respectively, within a 250-ms train and 3.0 ± 0.2 and 6.1 ± 1.3 s, respectively, within a 500-ms train. Biphasic dilations were observed within a 250-ms train at 20 Hz (at 3.9 ± 0.9 and 22.1 ± 4.3 s), 30 Hz (at 2.7 ± 0.3 and 17.5 ± 2.9 s), and 40 Hz (at 3.8 ± 0.4 and 23.2 ± 2.6 s) and within a 500-ms train at 20 Hz (at 4.8 ± 0.4 and 31.9 ± 3.8 s) and 30 Hz (at 3.4 ± 0.3 and 27.6 ± 3.0 s). A single dilation was observed within a 250-ms train at 60 Hz (at 5.1 ± 0.7 s) and 80 Hz (at 14.2 ± 3.3 s) and within a 500-ms train at 40 Hz (at 9.9 ± 3.2 s), 60 Hz (at 7.9 ± 2.1 s), and 80 Hz (at 13.4 ± 4.0 s). We have shown that a single contraction ranging from a single twitch (4 Hz, 250 ms) to fused tetanic contractions produces significant arteriolar dilations and that the pattern of dilation is dependent on the stimulus frequency and train duration.Key words: arteriole, skeletal muscle, hyperaemia, vasodilation, stimulus frequency.