Alteration of heart uncoupling protein-2 mRNA regulated by sympathetic nerve and triiodothyronine during postnatal period in rats

To provide tissue-specific and developmental characteristics of gene expression of rat heart uncoupling protein-2 (UCP2), we investigated developmental alterations of UCPs mRNA expression in the heart and brown adipose tissue (BAT), and examined possible up-regulators of heart UCP2 expression using in vitro studies. Heart UCP2 mRNA expression was low during the early postnatal days followed by a rapid and significant increase in the 2nd postnatal week. Heart UCP3 mRNA remained undetectable until the 2nd postnatal week when the expression reached a small but significant peak. BAT UCP1 mRNA was abundantly expressed in the neonate, but the expression rapidly decreased to the adult level. The studies using cultured cardiomyocytes demonstrated that both 10 −8 M triiodothyronine and 10 −7 M isoproterenol, but not phenylephrine, increased UCP2 mRNA expression. These results indicate that the sympathetic nervous system and/or thyroid hormones may be involved in the up-regulation of heart UCP2 gene expression during postnatal development. The increase in postnatal heart UCP2 may provide a key link between the postnatal energy shift and adaptation of rat pups to their novel environment.