Attenuation of vasodilatation with skeletal muscle fatigue in hamster retractor.

We tested the hypothesis that muscle fatigue would attenuate vasodilatory responsiveness throughout the resistance network. The retractor muscle of anaesthetized hamsters was contracted (once per 2 s for 1 min) at duty cycles of 2.5, 10 and 20 % before and after fatiguing contractions that diminished peak tension and muscle glycogen by >50 %. Arterioles and feed arteries (FA) dilated maximally during fatiguing contractions. Resting vasomotor tone consistently recovered following contractions. Peak blood flow was proportional to integrated tension (tension x time, expressed in mN mm-2 s); both increased with duty cycle and decreased with fatigue. Total integrated vasodilatory responses (diameter x time, expressed in microm s) increased with duty cycle and decreased with fatigue. Vasodilatation during contractions plateaued at approximately 50 % of peak integrated tension. Post-contraction vasodilatation increased with integrated tension and both were attenuated with fatigue. As integrated tension increased, distal arterioles dilated first and to the greatest extent relative to proximal arterioles and FA. Fatigue had little effect on dilatation of distal arterioles whereas dilatation of proximal arterioles and FA was suppressed. Latency of onset for vasodilatation decreased as duty cycle increased and was unaffected by fatigue. Vasodilatation and blood flow increase in proportion to integrated tension, with an ascending locus of vasomotor control and prolongation of post-contraction vasodilatation. With muscle fatigue, the locus of flow control resides in distal arterioles; both ascending and post-contraction vasodilatations are attenuated despite normal vasomotor tone.