Uterine Phosphorylase: In Vivo Activity is Inversely Related toin VitroInactivation*†

Sexually mature, intact, female rats were selected at various stages of the estrous cycle as determined by the vaginal smear method. Ovariectomized rats were treated with estrogen, orprogesterone or estrogen plus progesterone. Uterine tissues were frozen in situ then pulverized and mixed with powdered, frozen, extraction medium containing 0.1M NaF, 0.01M EDTA, and 60% glycerol, at liquid nitrogen temperature. These extracts were assayed for glycogen phosphorylase a and t activities. The rate of phosphorylase a inactivation in uterine homogenates was also determined as previously described (Rinard, G. A., Biochim Biophys Ada222: 455, 1970). The results indicated aninverse relationship between in situuterine phosphorylase a activity and in vitro rate of phosphorylase a inactivation. Baseline, in situ, uterine phosphorylase a activity in estrogen-treated ratswas twice that in rats treated with progesterone, with estrogen-plus-progesterone, or controls. Likewise, the activity in proestrus rats was twice that in diestrus rats. However, the rate of phosphorylase a inactivation in homogenates of uteri from proestrus rats was ¼ that from diestrus rats.These results taken together with previously published results indicate that stages of the estrous cycle or hormone treatments that produce increases in in situ phosphorylase a activity also produce decreases in the rate of inactivation of phosphorylase a in uterine homogenates. These data are compatible with the idea that the effects of steroids on uterine phosphorylase a activity may bemediated by effects on the uterine phosphorylase inactivating enzyme, presumably, phosphorylasephosphatase. (Endocrinology94: 1621, 1974)