Purine involvement in corpus luteum function in non-pregnant sheep

Abstract

Five experiments were done to discern the involvement of de novo synthesis of purines on ovine corpus luteum (CL) function, and to establish a model for assessing the in vivo effects of purines on CL function. In order to identify specific purine involvements, the adenylic, guanylic, and inosinic biosynthesis pathways were isolated using the de novo synthesis pathway inhibitors hadacidin, mycophenolic acid, and azaserine. In three in vivo experiments, these treatments were delivered into the sheath surrounding the ovarian vascular pedicle (OVP) ipsilateral to the ovary bearing the corpus hemorrhagicum via an exteriorized indwelling catheter. Delivery of the drugs to the CL by uptake into the vasculature was confirmed indirectly by HPLC analysis of luteal AMP, IMP, and GMP levels. Azaserine, hadacidin, or mycophenolic acid, or these drugs plus replacement compounds (inosine, adenosine, or guanosine, respectively), were delivered in phosphate buffered saline (PBS) via the OVP catheter at 4 or 6 hour intervals over days 1-7 or 1-8 post-estrus. Daily jugular blood samples were taken over the treatment period and quantified for estradiol-17γ and progesterone by RIA. CL, collected on day 7 or 8 post-estrus, were dissociated, and luteal cell populations and live/dead ratios of luteal cells were noted. Augmented profiles of progesterone and estradiol-17 γ were seen in ewes treated with 150 µg of azaserine, or mycophenolic acid, respectively, as compared to ewes treated with 500 µg of any of the drugs or controls. Estradiol-17γ and progesterone profiles for drug + replacement compound-treated animals were not different from control ewes. In vitro experiments involving incubation of luteal slices in PBS + luteinizing hormone (LH) with azaserine alone or combined with one of the pathway replacement compounds revealed that azaserine-treated luteal slices were able to produce progesterone levels that were not different from those produced either by controls, or adenosine-treated slices (amplifies LH-stimulated progesterone production). These data suggest that either a) the CL is less dependent on de novo synthesized purines than the readily available salvage pathway-derived purines, or that b) there may be a non-purinergic dependent second messenger system controlling biosynthesis of steroids in luteal cells.