Changes in Uterine Protein Synthesis during Delayed Implantation in the Western Spotted Skunk and its Regulation by Hormones

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Abstract
The uterine cornua of intact and castrate western spotted skunks were injected with 10 .mu.Ci of [3H]-Leu to study uterine protein synthesis during the 200-day preimplantation period and to determine the hormonal control of this process. The SDS [sodium dodecylsulfate] gels of skunk plasma and uterine flushings contained 2 bands (MW 43,000 and 14,000) that were never observed in plasma samples. Estradiol [E2] and/or progesterone [P] increased the quantity of the 14,000 MW component. The [3H]-Leu was incorporated into 2 protein fractions (fraction I with a MW of > 200,000 and fraction II with a MW of 43,000) during the early and late delay periods. The amount of radioactivity incorporated into fraction II quadrupled between the early and late delay periods. There was a significant increase in incorporation of label into 3 protein fractions .apprx. 5 days prior to nidation, with fraction III (MW 24,000) being present for the 1st time. Uterine protein synthesis did not occur in castrate females, whereas P significantly enhanced incorporation of precursor into fractions I, II and III, but did not replicate the condition observed during the early activation period. E2 alone or administered in conjunction with P significantly inhibited synthesis of labeled proteins. The preimplantation rise in P appears to play an important role in enhancing the quality and quantity of uterine proteins; other hormones may also be required to induce the complete pattern of protein synthesis observed just prior to nidation.