Intraovarian regulators of the ovulatory process. Studies in the rat and human

Abstract

LH stimulation of the preovulatory follicle results in extensive biochemical and morphological changes which lead to follicle rupture. Many redundant and parallel functioning mediator systems are involved in this process. The aims of this thesis were to examine roles of the transcription factor (TF), C/EBPb, cyclooxygenase (COX)-2 and progesterone (P) on ovulation. Gonadotropin-induced in vivo and in vitro perfused rat ovary models were used to study the effects of C/EBPb inhibition, using antisense (AS) technique. An ovulation rate decrease along with altered follicular morphology was seen. C/EBPb did not seem to be required for COX-2 induction. Secretion patterns of P and estradiol (E) into perfusion media were not affected by this inhibition. In vivo and in vitro rat follicle incubation models, as well as the in vitro perfused rat ovary model, were used to examine the effects of COX-2 inhibition, by NS-398, on ovulation and on measured levels of various mediators. A dose-dependent reduction of prostanoids and ovulation rate was demonstrated, although an incomplete linkage between inhibition of these mediators and ovulation rate was noted. No effect was seen on levels of intraovarian leukotrienes levels or on P or cAMP levels measured in media. COX-2 inhibition in the human was examined using the selective COX-2 inhibitor, rofecoxib (RX), during the periovulatory period. Women were followed for at least two menstrual cycles, one control cycle and another treatment cycle, with the use of ultrasound and hormone analysis. Evidence of delayed follicular rupture, without effects on peripheral sex steroids or gonadotropins, was noted after RX treatment in 4 out of 6 women. The time interval after LH, during which P is important for ovulation, was studied in perfused rat ovaries exposed to the P receptor (PR) antagonist Org 31710. PR activation appears to be important up to at least 3.5h after the LH surge. No effects were seen on P and E levels in the perfusion media. Decreased intraovarian activity levels of prostanoids and plasminogen activator, was seen in vitro perfused rat ovaries exposed to Org 31710 and in vitro perfusion. Expression patterns of C/EBPb and COX-2 in human follicular tissue was compared using immunohistochemistry and immunoblotting techniques. In dominant follicles from follicular phase, the highest levels of C/EBPb were seen in the thecal cell (TC) compartments, whereas the highest levels of COX-2 are seen in both TC and stroma compartments. C/EBPb is expressed in the granulosa cell (GC) layer of the newly ruptured follicles and in granulosa-lutein layers of corpora lutea. COX-2 was seen in GC and TC layer in the newly ruptured follicle and not in the CL. The studies in this thesis identify some important factors in human and rat ovulation. The findings verify the complexity of ovulatory control mechanisms as well as the redundancy of several involved mediators.