Biology of Reproduction, Vol 23, 588-594, Copyright © 1980 by Society for the Study of Reproduction

Uterus of the Rat During Early Progestation: Pyridine Nucleotide Activity and Its Relation to Preimplantation Changes in Pentose Cycle Activity

¹ Department of Physiology and Cell Biology, University of Kansas, Lawrence, Kansas 66045

Using a radiometric enzymatic recycling method, measures were made of nicotinamide adenine dinucleotide phosphate (NADP) in the endometrium of the uterus of the adult rat during the estrous cycle and the first 6 days of pseudopregnancy. Though the content of NADP/endometrium varied between 174 pmoles (metestrus) and 1031 pmoles (proestrus) during the cycle, no significant changes in the concentration of the cofactor were measured (14-19 pmoles/mg tissue). By contrast, both the content and concentration of NADP increased between Days 1-4 of progestation. Following a decline in cofactor concentration between proestrus and Day 1 (to 9 pmoles/mg), activity increased to a sustained peak of about 24 pmoles/mg between 2400 h on Day 2 and 2400 h on Day 4. Calculation of the ratio of NADP⁺/NADPH revealed no significant changes during the cycle, whereas during pseudopregnancy two peaks were observed: from 0.15 (proestrus) to 0.33 (Day 1), and from 0.15 (Day 2) to 0.29 during the Day 3-4 interval. Changes in NADP concentration and in the oxidized:reduced ratio during early pseudopregnancy coincided with two previously established peaks in activity of the hexose monophosphate path(HMP). Thus, the data lend strong support to an earlier proposal that the regulation of HMP activity in the uterus during early progestation is dependent on the availability of the pyridine nucleotide cofactor and not on the relatively stable activity of the enzymes in the initial steps of this path.

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ACKNOWLEDGMENTS This investigation was supported in part by grants from the University of Kansas General Research Fund and Biomedical Research Fund, and by NIH Grant HD 11797.