The effects of pre- and postweaning dietary protein levels of mitochondrial metabolism in developing liver and interscapular brown adipose tissue (IBAT) in rats.

Isoenergetic diets containing casein:carbohydrate:fat, 22:59:10% (control protein, CP), or 8:73:10% (low protein, LP), were fed to female rats during gestation and lactation and to offspring postweaning. Control fed rats were pair-fed to the LP-fed group. In the LP-fed group, body and liver weights were similar at birth but decreased at 10, 21, and 42 days, while intercapsular brown adipose tissue (IBAT) weight decreased from birth to 10 and 21 days but increased at 42 days compared to controls. Hepatic mitochondrial oxygen consumption (OC) with pyruvate + malate as substrate was similar at 21 and 42 days, whereas OC in state 3 and 4 with succinate was decreased at 42 days, only in the LP-fed group. In IBAT, OC was similar in each group at each age. In the LP-fed group, hepatic glycerolphosphate (GP) shuttle activity was the same as in controls at birth but increased progressively from 10 to 21 and 42 days, whereas malate-aspartate (M-A) shuttle activity was not substantially changed during development. In IBAT, shuttle activities were similar in both groups during development with M-A shuttle activity increased in the LP-fed group at 21 days. Serum triiodothyronine (T3) levels in the LP-fed group were increased at 10 and 42 days but decreased at 21 days after birth. These results suggest a role for both pre- and postweaning diet composition as a regulator of hepatic metabolism during development. The deficit in IBAT weight in the LP-fed group during early postnatal development indicates a decreased capacity for heat production in the neonate caused by maternal protein undernutrition.