The present study was designed to test the hypothesis that prostanoids play a permissive role in acetylcholine-induced cerebral constriction. Pial arterioles of newborn pigs were observed using a closed cranial window. Pial arteriolar constriction induced by topical acetylcholine (10(-5) M) was blocked by indomethacin (5 mg/kg i.v.), but was restored when acetylcholine was coadministered with topical prostaglandin (PG) F2 alpha (1 ng/ml), U46619 (1 ng/ml) or PGH2 (100 ng/ml). The restored acetylcholine response was blocked by topical pirenzepine (10(-3) M), a muscarinic-1 antagonist. Constriction and ability of all three prostanoids to restore acetylcholine-induced constriction was blocked by SQ 29,548 (10(-4) M), a purported thromboxane A2/PGH2 receptor antagonist. Subthreshold concentrations of U46619 and PGF2 alpha (0.1 ng/ml) restored acetylcholine-induced constriction, whereas threshold and subthreshold concentrations of PGE2, platelet-activating factor and norepinephrine had no effect. Therefore, activation of the thromboxane A2/PGH2 receptor appears to be necessary for acetylcholine-induced constriction to occur. Thus, prostanoids appear to play a permissive role in acetylcholine-induced pial arteriolar constriction in newborn pigs.