Vasoconstrictors alter oxygen, lactate, and glycerol metabolism in the perfused hindlimb of a rat kangaroo.

The Tasmanian bettong (Bettongia gaimardi) is a small marsupial rat kangaroo without detectable brown adipose tissue (BAT). The hindlimb was perfused with constant flow at 25 degrees C after cannulation under anesthesia of the femoral artery and vein to one hindlimb. Norepinephrine (NE, 25 nM-2.5 microM) and vasopressin (VP, 10 nM-0.1 microM) each increased perfusion pressure, oxygen consumption (VO2), and lactate and glycerol efflux of the perfused hindlimb. NE-mediated increases in VO2 and the efflux of lactate and glycerol were unaffected by propranolol (10 microM) but were completely blocked by the further addition of phentolamine (10 microM). In contrast, serotonin (5-HT; 0.1-2.5 microM) inhibited VO2 and inhibited lactate efflux. The changes induced by NE, VP, and 5-HT were all rapidly reversed by nitroprusside. These results suggest that resting thermogenesis in bettong hindlimb can be differentially controlled by the vasculature, which may also contribute to the induced VO2. This vascular control of skeletal muscle VO2 appears widespread in homeotherm evolution.