Structure and biological activity of gonadotropin-releasing hormone isoforms isolated from rat and hamster brains

Rat and hamster brain tissues were used to investigate the possible existen ce of a follicle stimulating hormone (FSH)-releasing factor with similar ch aracteristics to the lamprey gonadotropin-releasing hormone III (IGnRH-III) form proposed in previous reports. The present studies involved isolation and purification of the molecule by high-performance liquid chromatography (HPLC), identification by radioimmunoassay, sequence analysis by automated Edman degradation, mass spectrometry and examination of biological activity . Hypothalamic extracts from both species contained an HPLC fraction that w as immunoreactive to GnRH and coeluted with IGnRH-III and 9-hydroxyproline mGnRH ([Hyp(9)]GnRH). Determination of primary structure from purified tota l brain material demonstrated that the isolated molecule was [Hyp(9)]GnRH. This is the first report showing the presence of the posttranslationally mo dified form already known as [Hyp(9)]GnRH by primary sequence analysis. The biological activity of distinct GnRH peptides was also tested in vitro for gonadotropin release using rat pituitary primary cell cultures. The result s showed that [Hyp(9)]GnRH stimulated both luteinizing hormone and FSH rele ase, as already reported, whereas IGnRH-III had no action on the secretion of either gonadotropin. Copyright (C) 2001 S. Karger AG, Basel.