A Quantitative Study of the DNA and RNA in the Livers of Albino Mice During the Estrus Cycle

Several investigators have suggested that the nucleic acid content of mouse liver varied with the estrus cycle. Nucleic acids were extracted with trichloroacetic acid and ethanol. The quantity of DNA and RNA was determined with a spectrophotometer. No significant differences were observed in the quantity of DNA or RNA throughout the estrus cycle. Diversity in the amount of nucleic acids present among the livers of non-litter mates was one-third greater that that among litter mates. In studies of the nucleio acid content of mouse liver, little is gained by controlling the estrus cycle, but using litter mates is suggested to demonstrate small fluctuations. In the continuing attempt to understand carcinogenesis, any changes which occur during the induction of a neoplasm are of obvious interest. Hepatomas and cirrhosis of the liver have been induced by oral and intraperitoneal administration of carbon tetrachloride. Several workers (Stowell, et al., 1951; Tsuboi, et al., 1951) showed definite changes in the amount of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) present in such abnormal livers. Dudley, Coppock, and Johnson( 1959) demonstrated a difference in the nucleic acid content of normal livers and that of livers of mice fed carbon tetrachloride. However, this difference was largely obscured by the variation within the experimental and control groups. Factors such as age, enzymes, and hormones might cause a variation in the amount of DNA and RNA present in normal mice. Until these variables have been investigated, interpretation of the data pertaining to the effects of carcinogenic agents on nucleic acid content will be difficult. Spriggs ( 1963) found that the nucleic acid content of mouse liver varied accmding to age and he reported that a cyclic pheoomenon, suggestive of the estrus cycle, was evident in his data. Vadous effects on liver cells have been ascribed to gonadal hormones. Allan ( 1944) demonstrated that estrogen increased the number of binucleate liver cells in rabbits, but Bullough ( 1946) showed that esterone did not increase the number of mitoses in mouse liver cells. Bond ( 1961) described a protein found in the liver of only male rats. Bond suppressed this protein by castration and restored it by the ,administration of testosterone. Although Common, Chapman, and Maw ( 1951 ) 1 Graduate Assistant, Drake University, Des Moines.