diacylglycerol
Diacylglycerol is the “stay-behind” messenger of its pathway. While its partner IP3 floats off into the cytoplasm to release calcium, diacylglycerol stays anchored in the membrane and recruits an enzyme right there at the cell's edge.
It is the second of the two messengers made when phospholipase C splits a membrane lipid after a hormone activates a Gq-coupled receptor. Diacylglycerol's main job is to activate protein kinase C, an enzyme that, like protein kinase A, phosphorylates target proteins to change the cell's behavior. Protein kinase C usually also needs the calcium that IP3 has just released, so the two messengers act as a team.
Through protein kinase C, the diacylglycerol arm influences cell growth, secretion, and contraction, and it cooperates with the calcium signal triggered by IP3. Because both messengers come from the same lipid split, a single hormonal event can drive two coordinated responses at once.
GnRH acting on pituitary cells generates diacylglycerol and IP3 together, jointly driving the release of LH and FSH.
Diacylglycerol and IP3 working as a pair after one hormone signal.
Diacylglycerol stays in the membrane because it is fatty, while IP3 is water-soluble and travels through the cytoplasm — a neat division of labor from one parent lipid.