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Biology of Reproduction, Vol 13, 527-534, Copyright © 1975 by Society for the Study of Reproduction

Protein and RNA Synthesis in Endometrium of the Rat Uterus During Early Progestation

D. G. BLAHNA 1, and J. M. YOCHIM 1

1 Dept. Physiology and Cell Biology, University of Kansas, Lawrence, Kansas 66045


To assess the rate and timing of nucleic acid and protein synthesis in the endometrium of the rat during early progestation, two series of experiments were performed. Measures were made of a) the incorporation of labeled glycine into endometrial subcellular fractions and b) the uptake of labeled leucine and uridine into TCA-insoluble material of endometrium. Of the glycine incorporated during the cycle, 50-70 percent was distributed into the nuclear fraction, with 30-50 percent in the other two fractions. Following the induction of pseudopregnancy, about 97 percent of the label was associated with the nuclear fraction. By Day 4 of progestation, a shift in the distribution occurred, such that 68 percent of the glycine was associated with the soluble and mitochondrial fractions. Calculated as specific activity, different patterns of activity were evident in each fraction: 1) no changes occurred during the estrous cycle in the nuclear and mitochondrial fractions and 2) the soluble fraction showed peak activity during proestrus. Following cervical stimulation, a significant, transient rise in specific activity was measured on Day 1 in all three fractions. Subsequently, a second peak in activity occurred on Day 3 in the soluble and mitochondrial fractions. The data suggest that at the onset of progestation, a change in the ability of the tissue to utilize exogenous substrate may occur: glycine may be compartmentalized, and thus withheld from the general metabolic machinery of the cell, or it may be utilized preferentially in the biosynthesis of nucleic acid. Following this initial period, a greater proportion of label may be utilized in various other metabolic pathways.

Total incorporation of leucine and uridine showed similar patterns: peak activity, measured during proestrus, declined to minimal activity during estrus and metestrus. After stimulation of the uterine cervix, incorporation declined to a low level by Day 1 of pseudopregnancy. After Day 2, a significant increase occurred, which was maintained through Day 6. Calculated as specific activity, the incorporation of these substrates showed no significant day-to-day changes during the cycle. Following induction of pseudopregnancy, a more gradual decline in the specific activity of uridine was followed by a transiently increased leucine activity on Day 1, but the responses were marginal (and not significant). Between Days 2-5 a dramatic rise in the specific activity of both substrates was measured.

These experiments suggest that at the beginning of progestation the uterine endometrium generally reflects the effect of postovulatory hormone deprivation, though local changes in biosynthetic activity, induced by early progestogenic action may be evident. Following Day 2, however, a second, dramatic increase in the rate of biosynthetic activity occurs which can be measured as an increased rate of synthesis of RNA and protein, and increased protein content. These changes in endometrium, evident by Day 3, reach their peak before Day 4, the time of maximal sensitivity of the uterus to decidualizing stimuli.

 Submitted on February 5, 1975
Accepted on August 27, 1975






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Copyright © 1975 by the Society for the Study of Reproduction.