<prompt> Second messenger for oxytocin-cAMPcGMPIP3-DAGNO  <response>: Ans. is c i.e., IP3-DAGPhospholipase IP3 - DAG system Activation of phospholipase by stimulatory G protein hydrolyses the membrane phospholipid phosphatidyl inositol 4, 5 bisphosphate PIP2 to generate the second messenger inositol I, 4, 5 - triphosphate IP3 and diacylglycerol DAG. IP3 mobilizes Ca2 from intracellular organelles - increased cytosolic Ca2. DAG enhances Protein Kinase C activation by Ca2. Ca2 acts as third messenger in this type of transduction mechanism and mediates the physiological effects of drugs. Protein kinase-C phosphorylates various intracellular proteins threonine, serine or tyrosine residue, causing their activation or inactivation. Example - Growth hormone releasing hormone GHRH, Thyrotropin releasing hormone TRH, GnRh, ADH Vasopressin VI receptor, vasopressor action, oxytocin, cholecystokinin, PDGF, Gastrin, Catecholamines some actions via a1 receptors, Angiotensin II vascular smooth muscle, Substance P, Histamine - H1, muscarinic M1, M3 