Variations in uterine cytosolic oestrogen and progesterone receptor levels during the rat oestrous cycle.

The levels of cytosol receptors for both oestradiol and progesterone were simultaneous monitored in the uterus at various stages of the rat oestrous cycle. The use of the synthetic gestagen R-5020, with its high specificity and affinity for the progesterone receptor, eliminated interference arising from corticosteroid binding globulin (CBG) contamination of uterine extracts. The results show that the patterns for both receptors are markedly different over the cycle. The variation can be correlated with changes in ovarian steroid output. The results also suggest that oestradiol and progesterone interact not only with their specific receptor, but also influence the other receptor system.