Ghrelin is important in the control of gastrointestinal physiology whereas somatostatin is important in the regulation of diverse neuroendocrine functions. Based on bioinformatic analyses of evolutionarily conserved sequences, additional peptide hormones encoded by pro-ghrelin and pro-somatostatin were predicted and named as obestatin and neuronostatin, respectively. Obestatin was immuno-purified from the rat stomach to be an amidated peptide of 23 residues. Subsequently, obestatin was found as a brain/gut peptide hormone capable of regulating water drinking in rodents and pancreatic functions in cultured cells. After ip injection of obestatin, an early response gene c-fos was induced in the nuclei of gastric mucosa, intestinal villi, white adipose tissues, hepatic cords, and kidney tubules. In cultured 3T3-L1 cells, treatment with obestatin, but not motilin, also induced c-fos expression. In these preadipocytes, treatment with obestatin also stimulated ERK1/2 phosphorylation and the phosphorylation of Akt. Mono-iodo-obestatin, purified using HPLC, was found to bind to jejunum, stomach, ileum, pituitary, and white adipose tissue. Furthermore, human embryonic kidney 293T cells transfected with plasmids encoding human or mouse GPR39 receptor or a human GPR39 isoform, but not the ghrelin receptor, exhibited high-affinity binding to mono-iodo-obestatin. These findings indicate that obestatin is a metabolic hormone capable of binding to GPR39 to regulate the functions of diverse gastrointestinal and adipose tissues. Antibodies to neuronostatin were generated by Dr. J. K. Chang at Phoenix Pharmaceutical (Burlingame, CA) and immuno-affinity purification allowed the sequencing of an amidated neuronostatin peptide of 13 residues from porcine tissues. In vivo treatment with neuronostatin induced c-fos expression in gastrointestinal tissues, anterior pituitary, cerebellum, and hippocampus. In a human gastric tumor (KATO-III) cell line, neuronostatin treatment induced c-fos expression, stimulated serum-responsive element (SRE) reporter activity, and promoted cell proliferation. In vivo studies performed in anaesthetised animals further indicated that intracerebroventricular treatment with neuronostatin increased blood pressure in a biphasic manner but suppressed food intake and water drinking. These findings demonstrate diverse neuroendocrine and cardiovascular actions of a somatostatin gene-encoded hormone and provide the basis to investigate the physiological roles of this endogenously produced brain/gut peptide. The present bioinformatic approach based on the conservation of sequences for putative mature peptide hormones as well as their flanking amidation and convertase cleavage sites in diverse vertebrates allows the prediction of novel peptide hormones. Coupled with the purification of endogenous peptides and functional testing using both in vitro cell lines and in vivo models, one can elucidate the pharmacological actions and physiological roles of novel brain/gut peptide hormones.