Influence of estradiol on nucleic acids, respiratory enzymes, and the distribution of nitrogen in the rat uterus

1. 1. The influence of single and repeated subcutaneous injections of 5 μg. estradiol on the uterus of the adult ovariectomized rat was studied. 2. 2. Estradiol was found to promote extensive synthesis of uterine ribonucleic acid (RNA) in contrast to little or no increase in desoxyribonucleic acid (DNA). As a result, the ratio of DNA: RNA changed from 3.4:1.0 in the castrate to 1.3:1.0 at 48 hr. after a single injection. At that time, both uterine weight and RNA content were maximal. 3. 3. Four daily injections of estradiol increased the succinate Q O 22 and the ascorbate Q O 2 to 400% of the castrate level. After a single injection of estradiol, activity reached a maximum at 48 hr. and then decreased. The activity of both enzymes was found to decline progressively for more than 1 month after castration. 4. 4. Determination of nitrogen in the water-extractable, alkali-soluble, and collagen fractions of uteri showed that although estradiol induced prompt increases in the absolute amount of nitrogen in each fraction, increments in the water-extractable moiety were particularly large. Thus, at 48 hr. after a single injection, when peak values were observed, the absolute amount of nitrogen in each of the three fractions amounted to 214, 167, and 144% of the control, respectively. 5. 5. The daily injection of 1 mg. progesterone for four consecutive days failed to alter the nucleic acids, respiratory enzymes, or the distribution of nitrogen from the castrate condition. 6. 6. The simultaneous occurrence of extensive synthesis of RNA, together with increased respiratory and synthetic functions in the absence of comparable increases in DNA, suggests that estrogen-induced uterine growth is based for the first 48 hr. on cytoplasmic growth as opposed to hyperplasia and may involve significant increases in mitochondrial mass.