Quantity and calculated oxygen consumption during summit metabolism of brown adipose tissue in new-born lambs

Macroscopic dissection of new-born lambs of several breeds revealed that brown adipose tissue comprised approximately 1.5% of the body weight. The perirenal-abdominal and prescapular-cervical depots were by far the largest, and the overall distribution was largely consistent with that reported for other species, although there was no significant interscapular depot. The oxygen consumption of the brown adipose tissue in lambs was calculated to reach 70 ml/(g-h), which is consistent with published data for rabbit brown adipose tissue, in vivo, but 35 times higher than that for the same tissue in vitro. It was also calculated that a substantial portion, perhaps two thirds, of the lipid available for metabolism was stored outside the adipose tissue. The study also made it possible to examine the validity of methods of estimating blood flow through brown adipose tissue. Untenable venous blood oxygen saturations were calculated from results obtained using 86-Rb, but saturation calculated from results with the radio-active microsphere method were entirely plausible.