Effects of compensatory growth on milk protein gene expression and mammary differentiation.

This experiment was conducted to develop an understanding of mechanisms responsible for effects of a compensatory (stair-step) growth pattern on the expression of milk protein genes and mammary differentiation. One hundred thirty weanling female rats were randomly assigned to either a control or a test group (compensatory growth). Early lactating mammary tissues from the compensatory growth group showed an increase in the RNA:DNA ratio, protein:DNA ratio, DNA, RNA, and protein while exhibiting a decrease in the lipid content as compared with those of the control group (2.2, 1.6, 1.7, 3.8, 2.8, and 0.5 times, respectively). Mammary tissues from the compensatory growth group contained about 1.1- to 1.4-fold more total cytoplasmic mRNA for caseins and whey acidic protein than those of the control group. The compensatory growth pattern increased beta-casein mRNA accumulation, milk protein secretion, and amino acid uptake in mammary acinar culture (1.3, 1.3, and 1.1 times, respectively) compared with those of the control group. These results indicate that the compensatory growth pattern increases milk protein mRNA transcripts and may contribute to an increase in the functional activity of the mammary gland.