CONICET | Buscador de Institutos y Recursos Humanos

Abstract It is well known that Thyroid hormones are regulators of lipid metabolism and modulators of signal transduction in cells. They also regulate metabolism through transcriptional and post-transcriptional mechanisms. On the one hand, Triiodothyronine (T 3) is known to increase liver lipogenic enzyme gene expression both in vivo and in hepatocyte culture.However, conflicting results have been reported on the effect of T (3) on lipogenic enzyme gene expression in white adipose tissue. Some authors have found that T (3) exerts a stimulatory effect on lipogenic The author is member of the Carrera del Investigador Científico del Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina. Correspondence/Reprint request: Dra Maria Sofia Giménez, Bioquimica Molecular Facultad de Quimica Bioquimica y Farmacia, Universidad Nacional de San Luis, IMIBIO (CONICET) Avenida Ejercito de los Andes 950, Argentina. E-mail: mgimenez@unsl.edu.ar enzyme gene expression in white adipose tissue both in vivo and in tissue culture. However other authors have found that significant effects of T (3) on lipogenic enzyme gene expression were only observed in the presence of relatively high (pharmacological) concentrations of the hormone. HypoT produces a drastic decrease of triglycerides (TGs) in the milk of lactating rats, and decreases in liver TG synthesis and in circulating TGs, which along with reduced mammary uptake of fatty acids caused by decreased Lipoprotein Lipase expression, result in an impaired mammary output of TGs to the milk. Hyperthyroidism changes maternal liver and mammary lipid metabolism, with increased liver rate of synthesis and decreased mammary synthesis. These changes, along with the mild hyperthyroidism of the litters, may contribute to their reduced growth rate.Thyroid hormones are of vital importance in the regulation of arachidonate-containing phosphoinositides metabolism in the liver. Sustained elevation of diacylglycerol (DAG) and ceramide levels in liver cells of hypothyroid rats are essential prerequisites for disturbances in agonist responsiveness of hepatocytes. L-thyroxine activates a dual phospholipase pathway in a sequential and synchronized manner: phospholipase C initiates the DAG formation, and PKC mediates the integration of phospholipase D into the signaling response during the sustained phase of agonist stimulation. Thyroid hormones are necessary for the equilibrated lipid metabolism in different organs and different physiological states.