Hypothalamic regulation of lipid metabolism in the rat: effect of hypothalamic stimulation on lipogenesis

The rates of fatty acid synthesis and syntheses of other lipids were measured in vivo by determining 3H-incorporation from tritiated water or 14C-incorporation from [U-14C]glucose into white adipose tissues (WAT), brown adipose tissue (BAT) and liver, during electrical stimulation of the ventromedial hypothalamic nucleus (VMH) and the lateral hypothalamic nucleus (LH) of female rats. Electrical stimulation of the VMH markedly increased the rate of fatty acid synthesis and the conversion of glucose to total lipids, glyceride glycerol and phospholipids in interscapular BAT, but not in parametrial or retroperitoneal WAT. Conversely, on VMH stimulation, the syntheses of total lipids, glyceride glycerol and phospholipids from glucose in the liver decreased slightly, though not significantly. Electrical stimulation of the LH had no such effect. Administration of insulin increased the rate of fatty acid synthesis in both brown and white adipose tissues and in the liver. The rate of disappearance of [14C]glucose and the concentration of insulin in the blood were not changed significantly by stimulation of the VMH. These data indicate that electrical stimulation of the VMH, but not the LH, enhances lipogenesis in BAT preferentially through a mechanism not involving insulin, but probably through activation of sympathetic innervation of BAT. The physiological significance of the findings is discussed in relation to hypothalamic function in controlling non-shivering thermogenesis and obesity.