The incorporation of radioactivity from tritiated water into fatty acids has been used as a measure of the rate of fat synthesis in rat epididymal adipose tissue. Tissue removed from fasted-refed rats incubated in the presence or absence of glucose synthesized fatty acids at a rate comparable to that of normal tissue incubated with glucose and insulin. This high rate of synthesis was increased about 100% by the addition of insulin when glucose was present. When no substrate was added, insulin produced a 40% increase in the rate of fatty acid synthesis while decreasing glyceride-glycerol and lactic acid formation. It is concluded that insulin addition alters the metabolic disposition of carbohydrate arising from intracellular sources. Tissue from normally fed rats incorporated 5 times as much tritium from water into fatty acids when 20 mM pyruvate was provided as substrate as when 20 mM lactate was present. Insulin increased fatty acid synthesis in the presence of pyruvate by 40% and with lactate by 60%. The formation of radioactive CO2 from lactate-l-14C was increased 46% by insulin. Homogenates prepared from tissue exposed to insulin displayed 27% more pyruvate dehydrogenase activity than control homogenates and 53% more activity than homogenates of tissue exposed to epinephrine. It is suggested that the pyruvate dehydrogenase of adipose tissue is subject to hormonal regulation and that this regulation may account in part for the action of insulin on fatty acid synthesis from lactate, pryuvate, or endogenous sources. (Endocrinology86: 1368, 1970)
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Robert L. Jungas (1970) studied this question.