Identification of stage-specific and hormonally induced polypeptides in the uterine protein secretions of the mare during the oestrous cycle and pregnancy.
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Uterine secretions were obtained on Days 4, 8, 12, 14, 16, 18 and 20 of the oestrous cycle and early pregnancy. Acid phosphatase activity was significantly affected by day of the cycle, reaching a maximum at days 12-14 during the luteal phase and then declining to almost undetectable levels, by Day 20. In pregnant animals, activity continued to increase beyond Day 14. Two-dimensional polyacrylamide gel electrophoresis showed that albumin was a major component. However, a number of unique proteins of non-serum origin appeared in mid-cycle but had disappeared by Day 20. One of these was a basic protein indistinguishable in electrophoretic properties from the uterine acid phosphatase of the pig, uteroferrin, which is believed to be involved in iron transport from the uterine endometrial epithelium to the conceptus. These same polypeptides, including the putative uteroferrin, were also present in uterine flushings from pregnant animals until Day 20, and in flushings from ovariectomized mares treated with progesterone but not in those given only oestradiol-17 beta. Flushings from all ovariectomized animals contained a non-serum, acidic polypeptide (pI 5.3) of molecular weight 70 000. One basic polypeptide (molecular weight approximately 17 000) appeared by Day 4 of the oestrous cycle and disappeared by Day 16 but was maintained during pregnancy until Day 20. It was absent, however, in flushings from a Day 45 pseudopregnant mare. Like the sow, therefore, the mare possesses a number of proteins associated with cyclic changes in steroid hormones during the oestrous cycle and early pregnancy.
