Regulation of lipogenesis and of non-saponifiable-lipid synthesis in vivo at birth and after prolonged starvation in the newborn rat

Hormonal regulation of malic enzyme expression in primary cultures of foetal brown adipocytes

Insulin increased malic enzyme activity and protein content in foetal brown adipocyte primary cultures through a two fold increase in the rates of enzyme synthesis. Conversely, noradrenaline prevented the induction caused by insulin on enzyme expression through an accelerate rate of malic enzyme degradation. Tri-iodothyronine had no effect on the expression of malic enzyme in cultured foetal brown adipocytes.

Rates of lipogenesis in fetal hepatocytes in suspension and in primary culture: hormonal effects

Lipogenesis in isolated fetal hepatocytes in suspension for 3 h was modulated by insulin depending on substrates utilization, but was inhibited by glucagon and noradrenaline from all substrates studied. After primary culture for 5 days in the presence of glucose, the lipogenic response to insulin increased, the glucagon response decreased and noradrenaline produced the same degree of inhibition at 3 h. At 24 h, insulin produced an even higher increase on lipogenesis parallel to an increase in fatty acid synthase activity. Dexamethasone increased lipogenesis, but progesterone had no effect. Both hormones, in the presence of insulin, increased lipogenesis and fatty acid synthase activity. Triiodothyronine, alone or in the presence of insulin, increased lipogenesis and fatty acid synthase activity.

Hormonal regulation of rat foetal lipogenesis in brown-adipocyte primary cultures

Insulin stimulates lipogenesis by 100% for 5 h by a covalent modulation of acetyl-CoA carboxylase, and by 200% for 24 h by increasing malic enzyme and fatty acid synthase enzymic activities in brown-adipocyte primary cultures. At short times, noradrenaline and isoprenaline decrease lipogenesis. However, phenylephrine and glucagon have no effect. At long times, dexamethasone inhibits lipogenesis. This effect is precluded in the presence of insulin. Progesterone and tri-iodothyronine, alone or in the presence of insulin, produce a stimulation of the rates of lipogenesis.

Regulation of rat foetal lipogenesis in brown adipose tissue in vivo and in isolated brown adipocytes during the last day of, and after prolonged, gestation

Rates of lipogenesis in foetal isolated brown adipocytes from 22-day-pregnant rats were significantly increased by lactate plus pyruvate as major substrates in the incubation medium, in comparison with the endogenous rates. Insulin stimulated foetal brown-adipocyte lipogenesis, and adrenaline or noradrenaline and isoprenaline decreased lipogenesis. Glucagon had no effect on the lipogenic rate in brown adipocytes. Progesterone administration to the mother significantly increased the rates of lipogenesis in brown adipose tissue and in isolated brown adipocytes from 22-day foetuses. Prolongation of gestation by progesterone to day 23 decreased the rates of brown-adipose-tissue lipogenesis in vivo and in isolated cells in the post-mature foetuses.

Regulation of carnitine palmitoyltransferase activity in the liver and brown adipose tissue in the newborn rat: effect of starvation and hypothermia

The overt activity of hepatic carnitine palmitoyltransferase (CPT1) increased during the last day of gestation in the foetus and after prolonged starvation in the newborn kept at 37 degrees C. Its sensitivity to inhibition by malonyl-CoA decreased during the perinatal period studied. Brown fat CPT1 increased under the same experimental conditions. However, its sensitivity to malonyl-CoA remains unchanged. Hypothermia at 24 degrees C decreased in the liver and increased in brown adipose tissue CPT1 activity in response to fasting. Glucose injection at birth decreased CPT1 activity in the liver but did not have any effect in the presence of mannoheptulose. This effect of glucose was non-significant in brown adipose tissue.