Ovarian-independent fluctuations of estradiol receptor levels in mammalian tissues.

Three types of periodic fluctuation in tissue concentrations of estradiol receptor protein have been observed. A seasonal variation is described in the uteri of 12-16-week-old calves and of ovariectomized pigs, and in mammary tumor tissue obtained from postmenopausal women. A circadian rhythm has been demonstrated in uteri of ovariectomized rats. An irregular periodic fluctuation has been found in uteri of ovariectomized and of ovariectomized/hypophysectomized rats, with the period varying from 9 to 15 days. These observations establish that a substantial turnover of receptor occurs in the absence of hormone and that 'normal' baseline values of receptor concentration do not exist.