Expression of progesterone receptors in bovine corpus luteum during pregnancy

The expression of progesterone receptors and matrix ribonucleic acid in 37 corpora lutea in 1-7 month's pregnant cows was investigated. Corpora lutea were obtained from slaughtered animals. Progesterone receptors expression was confirmed using biotin-streptavidin immunohistochemistry. Matrix ribonucleic acid expression was studied using pyronin staining by Unna-Brashe method. The expression of progesterone receptors was the highest in the luteal cells of the one-month pregnancy corpus luteum. It decreased significantly (p<0.05) from the third to the fourth month of pregnancy, but there was no significant difference in the expression of progesterone receptors from the first to the second and from the second to the third month of pregnancy. Also, there was no significant difference in the expression of progesterone receptors from the fourth to the fifth month and from the fifth to the sixth month of pregnancy. The expression of matrix ribonucleic acid also decreased during pregnancy, but gradually, with no significant monthly differences. It decreased significantly (p<0.05) from the sixth to the seventh month of pregnancy only. Our study shows that both indices - progesterone receptors and matrix ribonucleic acid decrease in the steroidogenic luteal cells during pregnancy and that a strong linear correlation (r=0.88) exists between these indices.