A study of the uterine protein variations during the estrous cycle in the cow: Molecular weights determination

This study was carried out to investigate molecular weights (MW) of the uterine protein content as the first step in their identification, and their variations during the estrous cycle as a part of the uterine adjustments for provision of an appropriate environment for physiological events in the bovine. Of the 24 pro-estrous, 21 estrous, 24 met-estrous and 46 diestrous uterine fluid samples prepared for our previous work, five samples in each phase were selected randomly and subjected to SDS-PAGE analysis in parallel with standard marker proteins to separate their protein content into fractions. By comparing these fractions with those of the standards, MWs of <14.4, 20, 30, 38, 40, 46, 67, 75, 85, 90, 160, 200, 210, 270 and 330 kiloDaltons (kDa) were calculated, respectively. Proteins with MWs of less than 14.4 kDa [5.3 mg/ml (7.5% of total protein)] were observed only in met-estrus. Proteins with the MW of 20 kDa [14.0 mg/ml (19.4%)] were found only in diestrus. Proteins with MW of 30 kDa in met-estrus [20.6 mg/ml (28.9%)] and diestrus [4.5 mg/ml (6.3%)], and 38 kDa proteins were observed in a considerable amount in pro-estrus [41.4 mg/ml (44.5%)] and estrus [40.0 mg/ml (44.2%)]. Forty kiloDaltons proteins were observed only in diestrus [5.5 mg/ml (7.6%)], and 46 kDa proteins were observed only in met-estrus [5.3 mg/ml (7.6%)]. Sixty seven, 75 and 330 kDa proteins were observed in all the phases of the cycle with different densities, the higher values recorded in diestrus, pro- and met-estrus, respectively. Proteins with MW of 85 kDa were observed in all the phases but diestrus [9.8 mg/ml (10.5%), 8.6 mg/ml (9.5%) and 7.3 mg/ml (10.2%) for pro-estrus, estrus and met-estrus, respectively], and proteins with MW of 90 kDa were observed in estrus [20.0 mg/ml (22.1%)] and diestrus [3.3 mg/ml (4.6%)]. Proteins of 160 kDa fraction were observed in pro-estrus [9.8 mg/ml (10.5%)] and met-estrus [10.7 mg/ml (15%)], 200 kDa proteins were observed only in diestrus [6.3 mg/ml (8.7%)]; finally, 210 and 270 kDa proteins were observed only in estrus [3.4 mg/ml (3.8%) and 2.0 mg/ml (2.2%), respectively]. It was concluded that protein profile of the bovine uterine lumen changes during the estrous cycle, both in quality and quantity, which may be a part of uterine adaptation for the physiological events. Further identification of these proteins would give us a better insight into their role in the bovine reproduction.