Ovarian levels of epidermal growth factor receptor mRNA in the rat--a postovulatory decrease

Members of the epidermal growth factor (EGF) family have many different effects on ovarian cells including a strong inhibition of estradiol-17 beta production. An increased binding of the EGF family to its receptor is seen at the time of ovulation. The aim of the present study was to measure the mRNA levels of the EGF receptor in the preovulatory follicle and to see if the levels are still high after functional luteolysis. The mRNA of the EGF receptor was measured in whole ovaries, follicles and corpora lutea. Pregnant mare serum gonadotrophin (PMSG) stimulated rats were used to get defined follicles. To achieve luteolytic corpora lutea on day 11, the adult female pseudopregnant rat model was used. Determination of the EGF receptor mRNA was performed with solution hybridization analysis, using a 768 bp long probe of the human EGF receptor (2318-3085). A two-fold increase in the mRNA levels of the EGF receptor was registered between 09.00 and 21.00 h during the proestrus day in the preovulatory follicle. Concurrently, serum estradiol-17 beta levels decreased from 420 +/- 65 to 79 +/- 6 pM. High levels of EGF receptor proteins in the preovulatory follicle were verified by immunohistochemistry. The levels of EGF receptor mRNA was decreasing from 25.4 +/- 4.4 fmol mg-1 in the corpus luteum on day 1 to 7.6 +/- 9.9 fmol mg-1 on day 11. Thus, the high amounts of EGF receptor in the ovary during the late preovulatory period might be involved in the regulation of ovarian estradiol-17 beta production.