May play an important regulatory role in corticotrophs. Found in the lumen of secretory vesicles (dense core vesicles, DCV) (PubMed:17951542). However, seems to be retained intracellularly and not secreted (By similarity). Pituitary, hypothalamus and pancreas (PubMed:8132649). Found in alpha, beta and delta cells in the pancreatic islets (PubMed:17951542). Belongs to the RESP18 family.