Circulatory responses to 2,4-dinitrophenol in dog limb during normoxia and hypoxia

We tested whether blood flow to skeletal muscle would increase in proportion to an increase in O2 uptake caused by 2,4-dinitrophenol (DNP). We further tested the metabolic control in the face of a central challenge, hypoxic hypoxia. Three injections of DNP were made at 30-min intervals into the arterial supply of the left hindlimb in anesthetized dogs. Similar experiments were done on a second group of dogs ventilated with 12% O2-88% N2 (DNP and hypoxia). A third group served as time controls. Limb O2 uptake increased in a linear fashion in the DNP group with each injection. The increase in limb O2 uptake fell off with the second and third injections in the DNP and hypoxia group and appeared to be limited by the hypoxia. Limb blood flow increased only with the last injection in that group and not at all in the DNP group. Limb vascular resistance decreased in both the experimental groups relative to the time-related changes in the control group. This became more marked as the O2 extraction ratio exceeded 0.5. Even in the absence of nerve stimulation and active muscle contractions, both distribution and resistance control vessels responded in a coordinated fashion to an increase in O2 uptake. Mild hypoxia enhanced these responses but also appeared to limit a fraction of O2 uptake that may not have been concerned with maintaining tissue energy levels.