The phosphoinositide (PI) signalling pathway mediates noradrenaline (NA) and endothelin-1(ET)-stimulated vascular smooth muscle (VSM) contraction, through an inositol-trisphosphate-induced rise in intracellular calcium and diacylglycerol (DG) activation of protein kinase C (PKC). Subsequent activation of DG kinases (DGK) metabolises DG to phosphatidate (PA) potentially regulating PKC activity. Because precise regulation and spatial restriction of the PI pathway is necessary for specificity, we have investigated whether this occurs within caveolae/rafts, specialised plasma membrane microdomains implicated in VSM contraction. We show that components of the PI signalling cascade - phosphatidylinositol 4,5-bisphosphate (PIP₂), phosphatidic acid (PA) and DGK- are present in caveolae/rafts prepared from rat mesenteric small arteries. Stimulation with NA or ET induced [³³P]-PIP₂ hydrolysis solely within caveolae/rafts. NA stimulated an increase in DGK activity in caveolae/rafts alone whilst ET activated DGK in caveolae/rafts and non-caveolae/rafts; however, [³³P]-PA increased in all fractions with both agonists. Previously, we reported that NA activated DGK- in a PI 3-kinase (PI3K)-dependent manner; here, we describe PI3K-dependent DGK activation and [³³P]-PA production in caveolae/rafts in response to NA but not ET. Additionally, PKB, a potential activator of DGK-, translocated to caveolae/rafts in response to NA but not ET and PI3K inhibition prevented this. Furthermore, PI3K inhibition reduced the sensitivity of contraction to NA but not ET. Our study shows that caveolae/rafts are major sites of vasoconstrictor hormone activation of the PI pathway in intact small arteries and suggest a link between lipid signalling events within caveolae/rafts and contraction.