Cytoplasmic progestin receptors in myomal and myometrial tissues. Concentrations and hormonal dependency

Cytoplasmic progestin receptors in human myometrium and myomata of uteri, both with and without tumors, were determined. The same concentration was found in all tissues when expressed in terms of tissue weight or DNA content. However, tumors had slightly more receptors when calculated per mg of soluble protein. This was due to the fact that myomata contained considerably less soluble protein than the normal myometrium. The receptors present were dependent upon the serum concentration of estradiol. Increasing values were accompanied by an increase in the number of receptors. At estradiol levels exceeding 500 pmoles/l their number reached a plateau and became independent of the hormone concentration. Progesterone had no influence except at very high levels where it depressed the number of receptors significantly. The investigation did not reveal any difference in the number of or the hormonal regulation of cytoplasmic progesterone receptors present in the various tissues. However, it showed that tumors contained considerably less soluble protein than normal myometrium.