A nonocclusive cannula for sampling venous blood from the interscapular brown fat of conscious rats

Lack of an adequate method for sampling venous blood from the brown adipose tissue (BAT) of conscious animals has impeded study of the in vivo metabolism of this tissue during physiological activation of its thermogenic function. This paper describes a technique for cannulating the main vein (Sulzer's) of the interscapular BAT (IBAT) of rats in a manner that does not impair blood flow and allows multiple venous sampling over several hours in conscious animals. The technique was tested over the widest possible range of IBAT blood flows by applying it to measurements of IBAT arteriovenous O2 differences in barbital-anesthetized, cold-acclimated rats infused with vehicle or with various doses of noradrenaline. Comparison was made with controls in which samples of IBAT venous blood were obtained by cutting Sulzer's vein. Blood flow was measured by the microsphere method. These tests showed that the presence of the special cannula in Sulzer's vein had no significant effect on the blood flow, arteriovenous O2 difference, or O2 consumption of the IBAT at any level of noradrenaline-induced thermogenesis. The new technique will permit examination of the functioning of BAT in nonshivering thermogenesis and diet-induced thermogenesis under much more physiological conditions than hitherto possible. It should also significantly reduce the number of animals required for such studies.