The mechanism of gonadotropins and eicosanoids action in luteal cells is complex and not fully understood. The action of these agents may not completely be explained by cell surface receptor binding and activation of adenyl cyclase. These agents internalize and associate with receptors present in one or more of the intracellular organelles. In our efforts to determine the biological significance of nuclear gonadotropin and PGs binding sites, we have succeeded in demonstrating the presence of gonadotropin, PGE and PGF2a responsive nucleoside triphosphatase (NTPase), an enzyme involved in nucleocytoplasmic transfer of mRNA, in bovine luteal nuclear membranes. These findings raise a number of additional questions, which this grant proposal aims to answer. Briefly, the effect of gonadotropins and PGs on mRNA transport from isolated luteal nuclei, whether gonadotropin and PGs responsive NTPase plays a role in this transport and identification of transported mRNA using cDNA probes will be investigated. PGs also bind to nuclear membranes and stimulate NTPase activity. But this response has not been characterized in detail and it will be done in the present studies. Whether adenosine, which amplifies gonadotropins action with respect to cyclic AMP and progesterone production, can also amplify NTPase response to hCG and PGs will be examined. Basal NTPase activity and its response to gonadotropins and PGs during periods of rapid luteal growth, structural and functional maturity and regression and in corpora lutea rescued by establishment of pregnancy will be studied. Slices of corpora lutea will be incubated with and without gonadotropins and PGs and then nuclear membranes will be isolated for measurement of NTPase activity. NTPase in bovine luteal nuclear membranes will be solubilized and purified to answer whether this enzyme can bind gonadotropins and PGs and whether these ligands can stimulate the purified enzyme. The proposed experiments are a logical extension of our most recent findings. This project offers several new ideas and can potentially contribute novel concepts in the area of the molecular mechanism of gonadotropin and PGs action in corpus luteum. Such concepts do not necessarily conflict with the importance of cell surface binding in the action of gonadotropins and PGs and eventual degradation of ligands and/or their receptors in lysosomes of luteal cells. The new concepts can be complimentary to or additional mechanisms of gonadotropin and PGs action.
