Physiological Roles of a Novel Calcium Phospholipid Binding Protein, Annexin V,in the Function of the Anterior Pituitary Gland and the Ovary ; A Molecular-Cellular Biological Approach

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Physiological importance of a novel calcium-phospholipid binding protein, annexin V,in functions of the anterior pituitary gland and the ovary was investigated. By immunocytochemical approach, the specific distribution of annexin V on gonadotrophs at the anterior pituitary gland was demonstrated. The amount of this protein in the anterior pituitary gland was revealed to increase after ovariectomy. It was shown that ovariectomy enhances annexin V synthesis also by Northern blot analysis. These results led us to examine the effect of GnRH on annexin V synthesis and we found a stimulating effect of GnRH on annexin V mRNA accumulation. In turn, annexin V increased LH beta mRNA.Getting together, annexin V is thought to be a novel signal transducer of GnRH at pituitary gonadotrophs. Annexin V is hypothesized to be a physiological modulator also at the ovary. The distribution of annexin V was shown to restricted to luteal cells. Granulosa cells showed neither annexin V nor its mRNA.Furthermore, luteal annexin V varies its concentration along with pseudopregnancy. These results suggest annexin V would play a role in luteal progestational function. We also examined the effect of annexin V in neural system by observing single unit activity (SUA) recorded with a section of hypothalamus in vitro. Even though we have only preliminary data, annexin V was shown to inhibit or stimulate significantly the neural firing activity. The present project on the physiological role of annexin V raises a possibility that annexin V exerts specific activity locally in various tissues. Among these, its signal transducing action at gonadotrophs is the first observation on its activity of physiological modulator.