Delayed response of the mouse uterus to progesterone and oestradiol.

The delayed response of the uterus of the ovariectomized mouse to progesterone (P) required the presence of a low dose of oestradiol-17 beta (E2) and was associated with a maintained level of uterine DNA, an increase in RNA:DNA ratio and in total tissue protein and a decreased level of uterine P. This last parameter was associated with an increased level of in vitro metabolism of P by the uterus. Changes in the level of receptors for P and E2 were temporally unrelated to the delayed response. Omission of oestradiol every second, third or fourth day inhibited development of the delayed response, which could also be obtained with the long acting progestogen, medroxy progesterone acetate, and E2 or oestradiol benzoate.