Hypertrophy and hyperplasia of bovine fetal tissues during development: fetal liver insulin-like growth factor I mRNA...

Tissue growth of crossbred fetal beef calves was examined by measuring RNA, DNA, and protein concentrations in liver, heart, and biceps femoris. Furthermore, liver insulin-like growth factor I (IGF-I) mRNA expression and mRNA species size during fetal development was observed. Tissue samples were collected from six fetuses every 42 d of gestation, from d 106 to d 274. In the liver, protein and DNA concentrations decreased, whereas RNA levels remained constant throughout fetal growth. The RNA/DNA and protein/DNA ratios in liver increased with fetal age. Heart DNA and RNA levels decreased, whereas protein concentration and protein/DNA ratios increased with fetal age. Protein and protein/DNA ratios decreased in biceps tissue, whereas DNA and RNA concentrations were constant. IGF-I mRNA was seen at 4.4, 2.5, and 1.2 kb in adult and 4.4, 2.5, and 1.7 kb in fetal bovine liver. Relative expression of liver IGF-I mRNA did not vary during fetal development. The current study shows that during the last 2 and 3 mo of gestation, heart and liver were undergoing hypertrophic growth, whereas biceps tissue did not exhibit the same trend. Elevated ratios of RNA and protein to DNA in liver above that of the heart and biceps suggest extensive hepatic cellular hypertrophy as well as increased transcriptional and translational activity. Insulin-like growth factor I mRNA levels were not related to the changes in RNA, DNA, and protein seen in hepatic tissue.