BOVINE UTERINE, CERVICAL AND OVARIAN ESTROGEN AND PROGESTERONE-RECEPTOR CONCENTRATIONS

Bovine uterine cytosol estrogen (ERC) and progesterone receptors (PRC) were measured simultaneously in the endometrium and myometrium of cows with various serum progesterone concentrations. When serum progesterone concentrations were low (less than 2.7 nmol l-1), PRC concentrations in the endometrium (1162 fmol mg-1 cytosol protein) and in the myometrium (1315 fmol mg-1 cytosol protein) were relatively high. In animals with serum progesterone concentrations between 2.7 and 6.4 nmol l-1, endometrial and myometrial PRC concentrations were 695 fmol mg-1 protein and 694 fmol mg-1 protein, respectively. When the progesterone concentration was above 6.4 nmol l-1, PRC contents further decreased in endometrium and myometrium (491 fmol mg-1 protein and 485 fmol mg-1 protein, respectively). ERC concentrations seemed to follow those of PRC, but mostly the changes were not statistically significant. No differences were observed in PRC or ERC concentrations between the endometrium and myometrium at specified serum progesterone levels. Cervical PRC and ERC concentrations seemed to be lower than the corresponding uterine receptor levels and in the cervix, too, reduced PRC concentrations were associated with endogenous progesterone production. The latter finding strongly suggests that bovine uterine cervix tissue is under regulation by sex steroids. No differences in ERC or PRC contents were found between the two uterine horns of individual animals. Ovarian ERC and PRC concentrations were low compared to those detected in the uterus. Some synthetic C21-progestins were bound more avidly by the bovine PRC than by that of human, sheep, rabbit and guinea pig.