Isoprostaglandin F(2alpha) type-III (formerly known as 8-iso-prostaglandin F(2alpha)) is produced in large quantities in vivo in clinical situations associated with oxidant stress such as atherosclerosis, hypercholesterolemia, and myocardial reperfusion. Isoprostaglandin F(2alpha) type-III may alter smooth muscle and platelet functions. The aim of this study was to evaluate the effects of isoprostaglandin F(2alpha) type-III on isolated human internal mammary arteries, and to characterise the signalling underlying mechanisms. In organ baths, concentration-dependent contractions of human internal mammary arteries were obtained in response to isoprostaglandin F(2alpha) type-III stimulation. The responses to isoprostaglandin F(2alpha) type-III were inhibited in a concentration-dependent manner by the thromboxane A(2) receptor antagonist, GR 32191 ([1R-[1 alpha(Z), 2beta,3beta,5 alpha(+)-7-[[1, 1'-biphenyl)-4-yl]methoxy]-3-hydroxy-2-(1-piperidinyl) cyclo pentyl]-4-4heptanoic acid], hydrochloride), 3x10(-9) to 3x10(-7) M). However, this effect was associated with a decreased maximal contraction. AH 6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid, 10(-6) to 3x10(-5) M), an EP(1)-DP receptor antagonist had no effect on isoprostaglandin F(2alpha) type-III-induced contractions. The maximal responses to isoprostaglandin F(2alpha) type-III were significantly reduced in the presence of the cyclooxygenase inhibitor indomethacin (10(-5) M) (E(max): 147+/-20% vs. 213+/-19% in control group, P<0.05). Isoprostaglandin F(2alpha) type-III stimulated thromboxane B(2) release (5.7-fold increase) from human internal mammary arteries. Baicaleine, a non-specific lipoxygenase inhibitor, (10(-4) M) and AA 861 (2,3,5-trimethyl-6-(12-hydroxy-5, 10-dodecadiynyl)-1,4 benzoquinone), a 5-lipoxygenase inhibitor (10(-5) M) did not affect isoprostaglandin F(2alpha) type-III response. In conclusion, this study shows that (1) isoprostaglandin F(2alpha) type-III is a vasoconstrictor in human internal mammary arteries, with a potency equivalent to prostaglandin F(2alpha), (2) the contractions induced by isoprostaglandin F(2alpha) type-III are mediated by TP receptor but not EP(1)-DP-receptor activation, (3) thromboxane A(2) but not cysteinyl leukotrienes production is involved in the vascular effects of isoprostaglandin F(2alpha) type-III. Isoprostaglandin F(2alpha) type-III, produced at sites of free radical generation, may play an important role in internal mammary artery spasm in situations of oxidant stress such as coronary bypass surgery.