Phosphodiesterase inhibitor 3-isobutyl-methyl-xanthine affects rabbit ovaries and oviduct

The aim of our study was to examine the influence of 3-isobutyl-1-methyl-xanthine (IBMX), an inhibitor of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) phosphodiesterases on rabbit reproductive system. The ovarian cycle and ovulation of control rabbits were induced by gonadotropin releasing hormone (GnRH) or equine chorionic gonadotropin (eCG) followed by the human chorionic gonadotropin (hCG) administration. Experimental animals received GnRH together with IBMX (at 50 or 500 microg/animal) or eCG and hCG together with IBMX (at 5 or 257 microg/animal). After mating and insemination, blood samples were collected and analyzed for concentrations of progesterone and estradiol by RIA; some animals from the control and IBMX-treated groups were killed. The presence of follicles at different stages of development was evaluated by a light microscopy. Isolated ovarian fragments were cultured for 2 days. The secretion of progesterone and estradiol was assessed by RIA. The expression of markers of proliferation (PCNA and cyclin B1) and apoptosis (bax) in ovarian fragments was evaluated by Western-blotting. Epithelial cells were isolated from oviducts and cultured for 2 days. The expression of markers of proliferation (PCNA, ERK1,2-related MAP kinase) and apoptosis (bax, bcl-2) in the oviductal cells was evaluated by immunocytochemistry. It was observed, that the ovaries of rabbits treated with IBMX contained more secondary follicles, than control rabbits. Administration of IBMX reduced blood level of progesterone, but did not affect blood estradiol. Fragments of ovaries isolated from rabbits treated with IBMX released more estradiol, but not progesterone, than ovarian cells isolated from the control animals. IBMX injections substantially decreased the expression of the upper (23 kD), but not the bottom (24 kD) fraction of bax. IBMX administration did not affect PCNA, but it caused a decrease in the upper fraction (54 kD) and an increase in the bottom fraction (55 kD) of cyclin B1. Oviductal cells isolated from the IBMX-treated animals, contained less marker of apoptosis - bax (but not bcl-2) and proliferation - ERK1,2-related MAP kinase (but not PCNA) than control animals. These observations demonstrate the involvement of cyclic nucleotide-dependent intracellular mechanisms in control of rabbit reproductive functions: ovarian folliculogenesis, apoptosis, proliferation and steroid hormone release, as well as proliferation and apoptosis of the oviductal cells.