Bovine cerebral microvessels (arterioles and capillaries) synthesize prostacyclin (PGI2, measured as 6-keto PGF1 alpha), PGF2 alpha, PGE2 and thromboxane A2 (measured as TXB2) when incubated in glucose-bicarbonate buffer for 30 minutes. Rapid freezing and thawing decreased the subsequent synthesis of 6-keto PGF1 alpha by cerebral microvessels and raised the basal levels of this metabolite within the incubation medium. At low concentrations, the addition of arachidonic acid (0.16 microM) did not stimulate prostacyclin or prostaglandin production; at higher concentrations (16 microM), the synthesis of PGI2 and PGF2 alpha was inhibited. Activation of lipase by the peptide melittin stimulated the synthesis of all arachidonic acid metabolites to the same extent. Thus cerebral microvessels deacylate cellular lipids and metabolize endogenous arachidonic acid to form prostaglandins, prostacyclin and related compounds as previously demonstrated in larger blood vessels. The synthesis and release of these molecules may be important for modulating the tone and reactivity of small blood vessels within the brain.