The role of prolactin in realization of estradiol action in the uterus of ovariectomized rats.

The aim of this study was to examine the role of prolactin (PRL) in promoting the effects of estradiol (E2) on the uterus. Ovariectomized rats were given a single injection of E2 dipropionate (10 micrograms/rat), along with injections of ovine prolactin (PRL; a single dose--2.5 IU/rat), or injections of metoclopramide (a single dose--0.5 mg/rat), or injections of bromocriptine (a single dose--0.25 mg/rat). The effects of E2 on the uterus were determined by measuring mitotic indexes; cell, nucleus and nucleolus volumes (morphometry), and DNA content (Feulgen's method) in luminal and glandular epithelia, endometrial stromal cells at 24, 36 and 48 h after the injection of E2. It is revealed that at each time point after E2 and PRL or metoclopramide treatment almost all the tested parameters were lower than those in control rats treated with E2 and distilled water. The values obtained in all the periods after E2 along with bromocriptine treatment were higher compared with those in E2-treated animals. Most of the results are statistically significant (P < 0.05-0.001). In the absence of E2 none of the drugs used influenced the uterine parameters tested. The effect of PRL is likely to be mediated by their receptors in the uterus, and it occurs by changing the mechanism of estrogen action in the uterus. The actions of metoclopramide and bromocriptine are probably also mediated by PRL.