Identification of stage-specific and hormonally induced polypeptides in the uterine protein secretions of the mare during the oestrous cycle and pregnancy.

The research investigates the changes in uterine protein secretions in mares during different stages of the oestrous cycle and early pregnancy, identifying the presence of stage-specific and hormone-induced proteins. The study finds that the pattern of these proteins varies with albumin being a major component and several unique proteins, including a specific protein involved in iron transport, appearing during mid-cycle and disappearing by Day 20.

Methodology

• The researchers collected uterine secretions from mares on Days 4, 8, 12, 14, 16, 18 and 20 of both the oestrous cycle and early stages of pregnancy.
• They used two-dimensional polyacrylamide gel electrophoresis, a technique for separating proteins according to their size and charge, to analyze protein composition of the secretions.
• Uterine flushings from ovariectomized mares treated with progesterone were also studied, along with those given only oestradiol-17 beta.

Findings

• Acid phosphatase activity, a process that breaks down proteins into smaller units, was found to peak at days 12-14 during the luteal phase of the oestrous cycle and then decline to almost non-detectable levels by Day 20.
• In pregnant mares, this activity continued to increase beyond Day 14.
• Uterine secretions mainly contained albumin, a common protein found in blood plasma.
• Several unique proteins, not originating from the serum, were observed to appear around the mid-cycle and disappear by Day 20.
• One of these proteins was identified as uteroferrin, an acid phosphatase present in pigs that is believed to help transport iron from the uterus to the developing embryo.

Implications

• The findings suggest that mares, like pigs, possess specific proteins associated with changes in steroid hormones during the oestrous cycle and early pregnancy.
• Some proteins, including the putative uteroferrin, were present until Day 20 of pregnancy in uterine flushes from mares and those from ovariectomized mares treated with progesterone.
• This research provides insights into the regulation of protein secretion during different stages of the reproductive cycle in mares, which can help optimize breeding strategies in horses.