[Free tyrosine and progesterone receptor contents in the rat uterine endometrial cytosol during oestrous cycle].

Free tyrosine in the rat uterine endometrial cytosol at different phases of the oestrous cycle was measured by HPLC. It was found that the content of tyrosine varied at different phases of the oestrous cycle in the normal rat, i.e. being lowest in proestrus and highest in metestrus, while the progesterone receptor content in the same cytosol sample determined by radio-receptor technique showed an opposite relationship. Experiments showed that the tyrosine content and progesterone receptor content displayed periodic but opposite changes at the two phases of the oestrous cycle. Furthermore, administration of tyrosine to the uterine lumen decreased significantly the contents of progesterone receptor in proestrus, oestrus and diestrus, but not in metestrus. It is suggested that tyrosine might exert a certain regulatory influence on the progesterone receptor content in rat uterine endometrium.