Protein and RNA biosynthesis in various cellular fractions of the brain of undernourished rats

Abstract

Body and brain weight; DNA, RNA, and protein content; total free nucleotides; amino acids and their specific activities; as well as the in vitro incorporation of 14C-phenylalanine into protein and of 2H-orotate into RNA of homogenates and various cellular brain fractions were measured in well-fed (WF) and undernourished rats during gestation (EI) and during growth, gestation, and lactation (EII). Body weight was significantly decreased in both EI and EII while brain weight and DNA content per organ were lower in EII than in WF and EI rats. The brain weight:DNA ratio was increased significantly in EII animals compared with the WF group. RNA content did not show any significant alterations in homogenates, nuclear, microsomal and pH-5 enzyme fractions but was elevated in mitochondrial and soluble fractions of the brain of EI rats compared with the WF group. Brain RNA content in EII animals was decreased in homogenates and all cellular fractions with the exception of the nuclear fraction in which it did not change significantly. The RNA:DNA ratio tended to increase (non-significantly) in the EI and EII groups as compared with the WF controls. Protein content was decreased in homogenates and all cellular fractions of EII rats while it was reduced only in the mitochondrial and pH-5 enzyme fractions of the EI group. The RNA:protein ratio fell in the microsomal fraction and rose in the soluble and pH-5 enzyme fractions of EI and EII animals. The protein:DNA ratio increased significantly in homogenates and the nuclear fraction of the EII Group: 14C-phenylalanine/mg protein incorporation was augmented in homogenates, mitochondrial, and soluble fractions, was diminished in the microsomal fraction, and did not change in the nuclear fraction of the brain of EI and EII rats. 3H-Orotate/mg RNA incorporation was decreased in the nuclear and microsomal fractions and was increased in the soluble and pH-5 enzyme fractions of the brain of EI and EII groups. Incorporation was also elevated in brain homogenates of EII rats and was reduced in the EI group. It was increased in the mitochondrial fraction of EI animals but did not show any change in the EII group. From these results, it can be concluded that dietary stress during gestation alone (EI) and during growth, gestation, and lactation (EII) modulates the metabolism of nucleic acids and proteins in the whole brain and in various cellular brain fractions.