Biosynthesis of gonadotropin releasing hormone (GnRH): present status

Although the mechanism of GnRH synthesis has not yet been elucidated, many experimental data argue in favour of a ribosomal pathway resulting in the biosynthesis of a precursor with a size larger than the decapeptide. The existence of high mol. wt (HMW) immunoreactive forms of GnRH in hypothalamic extracts has been reported but without any evidence that they are precursors of the hypothalamic hormone. Some results obtained with immunocytological methods also suggest that at least a part of immunoreactive GnRH in perikarya might be extended on one or both its terminal ends. In our laboratory, we first investigated the process of GnRH biosynthesis in vivo by infusing tritiated amino acids into the third ventricle of rats. The results, along with the demonstration of the existence of HMW GnRH, support a ribosomal mechanism of GnRH synthesis. Also, preliminary data from our laboratory demonstrate that poly (A+) enriched RNA preparations from rat hypothalami contain compounds capable of hybridizing to a synthetic oligodeoxynucleotide probe which is complementary to a part of the GnRH sequence.