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The functional role of secretin outside the gastrointestinal system has been a mystery to endocrinologists for many years. With the availability of secretin- and secretin receptor-knockout models and the advances of electrophysiological and immunohistochemical techniques, we are now in a good position to explore the functions of secretin outside the gastrointestinal system. There is growing evidence to support that secretin works pleiotropically at multiple levels in our body. In this paper, we review the recent findings regarding the physiological effects of secretin on extragastrointestinal sites including the cerebellum, the hippocampus, and the hypothalamus-pituitary-kidney axis. To understand the mechanisms underlying the site-specific expression of secretin and secretin receptors in the central nervous system, we also discuss the transcriptional regulation of secretin and secretin receptor genes in neuronal cell lines. [ABSTRACT FROM AUTHOR]

Glucagon and the glucagon-like peptides (GLP-1 and GLP-2) share a common evolutionary origin and are triplication products of an ancestral glucagon exon. In mammals, a standard scenario is found where only a single proglucagon-derived peptide set exists. However, fish and amphibians have either multiple proglucagon genes or exons that are likely resultant of duplication events. Through phylogenetic analysis and examination of their respective functions, the proglucagon ligand-receptor pairs are believed to have evolved independently before acquiring specificity for one another. This review will provide a comprehensive overview of current knowledge of proglucagon-derived peptides and receptors, with particular focus on fish and amphibian species. [ABSTRACT FROM AUTHOR]