Integrated procedure for the determination of free fatty acid, glycerol, triacylglycerol and prostaglandins in rat epididymal fat pads

Dans le tissu adipeux brun du rat nouveau-né, on observe des augmentations des taux intracellulaires et de la production des prostaglandines E₂ et Fα, seulement au cours des 2 premiers jours. La production, in vitro, des PGs est stimulée par l'AMP cyclique, mais aussi par la noradrénaline par l'intermédiaire des récepteurs α adrénergiques.

In brown adipose tissue of newborn rat, the production and the intracellular level of prostaglandins E₂ and Fα are increased only on the first two postnatal days. The, in vitro, PGs production is stimulated either by cyclic AMP or by norepinephrine via α adrenergic receptors.

• 1.

  1. The increased lipid metabolism induced by cold acclimation of the rat results in a decrease in body fat stores and in an enhanced turnover of body lipids.

• 2.

  2. As indicated by lipoprotein lipase activity, the capacity for blood lipid uptake is increased in muscle and heart, and above all, in brown fat.

• 3.

  3. A large enhancement of lipogenesis from glucose is observed in the latter tissue and a lesser one in the liver and white fat.

• 4.

  4. The in vivo fatty acid mobilization from white fat by lipolytic hormones is enhanced, but in vitro the effect of these hormones on lipolysis and cyclic AMP production is reduced in brown adipocytes. A precise regulation of fatty acid liberation in brown fat could be postulated, the mechanism of which is unknown.

• 5.

  5. The ability of brown fat to produce heat by means of a decrease in mitochondrial respiratory control due to an increased membrane proton conductance is greatly enhanced by cold acclimation. However, the mechanisms of cyclic nucleotide—or fatty acid—dependent regulation of heat production in brown fat are hypothetical under physiological conditions.

A new micro-method was used to determine the effects of cold acclimation of rats on the levels of prostaglandins E₂ and F_α in both white and brown adipose tissues. Whereas PGF_α levels were significantly higher than PGE₂ levels in white fat, no difference between the amounts of the two prostaglandins was observed in brown fat. In both tissues, cold acclimation did not induce any change in prostaglandin levels.