The effect of vasoconstrictors on oxygen consumption in resting and contracting skeletal muscle of the autologous pump-perfused rat hindlimb.

This study used a novel in vivo model to test the hypothesis that nutritive and non-nutritive blood flow distribution can still be observed under conditions of high vascular tone and oxygen delivery at rest and in metabolically active (twitch contracting) skeletal muscle. Experiments were performed in a constant flow autologous pump-perfused hindlimb in anaesthetised male Wistar rats. Agonists were tested at rest with a flow rate of 1ml x min(-1), and during hindlimb muscle twitch contractions (sciatic nerve stimulation: 6V, 1Hz, 0.05ms, 3min) at a flow rate of 2ml x min(-1). Oxygen consumption was determined from hindlimb venous and arterial blood samples. Resting perfusion pressure at 1ml x min(-1) was 92 + or - 3 mmHg (N=15) and oxygen consumption was 0.41 + or - 0.05 micromol x min(-1) x g(-1). Serotonin increased perfusion pressure and significantly decreased basal hindlimb oxygen consumption at rest. During acute muscle contraction this effect on oxygen consumption was diminished. Noradrenaline significantly increased perfusion pressure but had no significant effect on basal hindlimb oxygen consumption. Vasoconstriction that impacts upon muscle metabolism occurs in vivo, which potentially could be due to selective redistribution of blood flow. However, during muscle contraction local release of vasodilatory regulation can overcome exogenously-induced vasoconstriction. These results support the hypothesis that dual vascular pathways may explain differential vasoconstriction and how it impacts upon muscle metabolism.