Exocytosis
The cellular process of releasing molecules from a cell by fusing intracellular vesicles with the cell membrane. Exocytosis is the mechanism by which hormones (including peptide hormones like insulin, GH, and oxytocin) are secreted from endocrine cells. GLP-1 receptor agonists stimulate insulin exocytosis from pancreatic beta cells.
Technical Context
Regulated exocytosis: stimulus-dependent secretion from specialised cells. In the context of peptide therapeutics: GLP-1R activation on pancreatic beta cells → cAMP/PKA and Epac2 pathways → potentiation of glucose-stimulated insulin granule exocytosis (the molecular basis of GLP-1 RA glucose-dependent insulin secretion); GHRH receptor activation on pituitary somatotrophs → cAMP/PKA → GH granule exocytosis; GnRH receptor activation on gonadotrophs → IP3/calcium → LH/FSH granule exocytosis (pulsatile GnRH drives this; continuous GnRH ultimately depletes granule stores contributing to downregulation). Molecular machinery: SNARE complex (v-SNARE on vesicle/VAMP + t-SNAREs on target membrane/syntaxin + SNAP-25) drives membrane fusion; calcium sensor synaptotagmin triggers fusion in response to calcium influx. Understanding the exocytic machinery contextualises how peptide drugs stimulate hormone release — they amplify or modulate the natural secretory process rather than directly causing non-physiological hormone release.