May play an important regulatory role in corticotrophs. Found in the lumen of secretory vesicles (dense core vesicles, DCV) (By similarity). However, seems to be retained intracellularly and not secreted (PubMed:7988462). Pituitary, hypothalamus and pancreas. Highest levels are found in somatotrophes, mammotrophes, and gonadotrophes, and lower levels are found in corticotrophs and thyrotropes. Up-regulated by high levels of glucose. Belongs to the RESP18 family.