Peptides represent a major mode of chemical transmission in the nervous and endocrine systems. Our studies have focused upon the LHRH prohormone as a model system to study the regulation of biosynthesis, processing, and secretion of neuropeptides. Previously, we have described the metabolic pathway for the pro-LHRH peptide in rat brain and have shown that gonadal steroids influence the biosynthesis and secretion of the major pro-LHRH products: LHRH and GAP. More specifically, gonadal steroids selectively affect both protein kinase C (PKC) activity and PKC-coupled secretion of LHRH and GAP. Recently, we have obtained a neuronal cell line, developed at the Salk Institute, which secretes LHRH-like peptides. When materials in cell extracts or media are separated by size-exclusion chromatography and assayed by radioimmunoassay, these cells are found to biosynthesize the pro-LHRH peptide, to process this precursor to LHRH and GAP, and to secrete these peptides into the media in response to PKC activation and [K+]-depolarization. When these cells are examined by EM, both LHRH and GAP immunoreactivity are co-localized in the same secretory vesicle. These cells form synapses and tight junctions with each other. These structural features provide a functional basis for the rhythmic and pulsatile secretion of LHRH that we have observed. These findings demonstrate that the LHRH neuron contains a pulse generator which may entrain the gonadotrophs of the pituitary to secrete LH in a pulsatile manner. Future studies will examine in detail the molecular mechanisms which regulate biosynthesis of the pro-LHRH peptide, the steps involved in its processing, and the various pathways of its secretion.
