Adrenergic neurohumoral influences on FFA release from bone marrow adipose tissue

It is well known that both the sympathetic nervous system and several hormones control adipose tissue lipolysis. However, the relative importance of these different lipolytic agents may vary according to the animal species and according to the adipose territories in a same species. The action of noradrenaline administration on tibial intraosseous lipolysis was compared with the effects of splanchnic nerve and lumbar sympathetic chain stimulation in chloralose-anaesthetized dogs. The osseous nutrient artery was infused through the homolateral femoral artery in order to check constant blood flow. The levels of free fatty acids (FFA) were compared in femoral artery blood and in the osseous nutrient vein. Noradrenaline was injected in the infusion line. Lumbar sympathetic chain and splanchnic nerve were stimulated at frequencies of 3-10 Hz and 5-10 Hz respectively. Noradrenaline (at 411 p mol/min i.e. a dose three times higher than that required for adrenaline) induced FFA mobilization from tibial adipose bone marrow. Splanchnic nerve stimulation elicited an increase in the FFA levels in the nutrient vein whereas lumbar sympathetic chain stimulation had no remained without any effect. It is concluded that circulating adrenaline seems more important than noradrenaline released by sympathetic nerve endings in the control of activity of tibial bone marrow adipocytes.