Rat Fetal Brown Adipose Tissue <i>in vitro</i>: Effects of Hormones and Ambient Temperature

Abstract

Interscapular brown adipose tissue (BAT) from fetal rats was maintained in Eagle’s minimal essential medium for 6–24 h at 37 or 25 °C. Pyruvate kinase (PK), cytoplasmic and mitochondrial α-glycerophosphate dehydrogenase and phosphoenolpyruvate carboxykinase (PEPK) activities were determined at the start and end of incubation. During prenatal development, the activities of all enzymes, except PK, increased significantly. During incubation at 37 °C, PEPK activity decreased by about 60% in 24 h. The other enzyme activities also fell to a lesser extent. Only the mitochondrial enzyme remained unchanged. Both glucagon and insulin significantly slowed down the fall in PEPK activity. Norepinephrine added every hour for 6 h increased PEPK activity, but only in BAT from fetal rats weighing less than 3.5 g. Incubation at 25 °C largely prevented the decrease in enzyme activities seen at 37 °C. Fetal liver reacted in the opposite way. At 37 °C, PEPK activity increased while at 25 °C it decreased. However, postnatal liver responded to incubation temperature like fetal BAT. It is postulated that the initial level of PEPK (high in fetal BAT and postnatal liver and low in prenatal liver) plays a role in the in vitro response.

CCAAT/enhancer-binding proteins α and β in brown adipose tissue: evidence for a tissue-specific pattern of expression during development

“…BAT contains substantial amounts of proteins such as GLUT4 glucose transporter (James et al, 1989) or PEPCK (Zimmer and Magnuson, 1990), whose gene expression is activated by C/EBP proteins in 3T3 white adipocytes (Kaestner et al, 1990) or liver (Park et al, 1990) respectively. The pattern of expression of these genes in BAT during development or cold exposure (Frohlich et al, 1976;Santalucia et al, 1992;Nikami et al, 1992), together with present data, suggest that C/EBP proteins may also regulate them in BAT. In conclusion, the present study shows a specific regulation of the expression of C/EBPa and C/EBP,3 genes in rat BAT during ontogenesis and in the physiological response to cold. As C/EBP isoforms may form heterodimers, changes in their abundance and in the C/EBP,/: LIP ratio provide further support for a functional significance of accumulation in vivo of these transcriptional variants in regulating BAT gene expression.…”