Body composition, food intake, and brown fat thermogenesis in pregnant Djungarian hamsters.

Strategies for balancing energy storage and expenditure during pregnancy were examined in the Djungarian hamster. In expt 1, pregnant hamsters lost nearly 50% of their body lipid stores, even though they showed significant increases in body weight and food intake during the latter half of pregnancy. The increase in body weight was accounted for by the growth of the uteri, fetuses, and placentas. The water and fat-free dry contents of the maternal carcasses did not differ from those of the unmated controls. In expt 2, brown fat cytochrome-c oxidase activity (mitochondrial content) was significantly lower in the late- but not early-pregnant females relative to the nonpregnant controls. Specific GDP-binding levels did not differ significantly among these groups. Thus an overall decrease in total thermogenic activity in brown fat would be expected during late pregnancy. The loss of carcass lipid, despite decreased brown fat thermogenesis and increased food intake, suggests that substantial increases in energy expenditure occur in pregnant females that are not related to heat production in brown fat. The present results are not consistent with traditional models of energy balance during pregnancy. Some of the inconsistencies may be related to differences between hoarding and nonhoarding families of rodents, whereas others may be due to the fact that the traditional model is based on a possibly exceptional species, the laboratory rat.