Localization of a peptide sequence contained in the precursor to gonadotropin releasing hormone (GnRH)

The precursor protein that contains the sequence for the neurohormone gonadotropin releasing hormone (GnRH) also contains an additional fragment (amino acids 14-26, designated pHGnRH14-26) that can release luteinizing hormone (LH) and follicle stimulating hormone (FSH) in vitro. An immunocytochemical study was carried out to determine if this sequence could be found in its processed form in hypothalamic nerve terminals. In rats, ewes and rhesus monkeys pHGnRH14-26 was demonstrated in both neuronal cell bodies and in axon terminals. In mice, immunoreactivity was present in terminals only. No reaction was found in the hamster hypothalamus. Double label immunocytochemical studies for GnRH and pHGnRH14-26 showed that both sequences could be found in the rat septal-preoptic-hypothalamic continuum in some but not all neuronal cell bodies. Control experiments strongly suggest that the 14-26 immunoreactivity represents the fragment after it has been cleaved from the precursor protein and that this peptide could be available for release into the hypophysial portal system.