We therefore designed the present study to evaluate the effect of S-adenosyl-L-methionine (SAMe) on the synthesis of platelet thromboxane and vascular prostacyclin. The experimental materials were human blood and aortic rings from untreated Wistar rats; and platelets and aortic rings from Wistar rats treated for 7 days with SAMe at 5 or 10 mg/kg/day s.c. The administration of 10 mg/Kg/day of SAMe to rats significantly increased vascular production of 6-keto-PGF1alpha. In vitro vascular production of 6-keto-PGF1alpha increased in a concentration-dependent manner when SAMe was incubated in the range of 10(-7) to 10(-4) M. The greatest increase was 167 +/- 15%, obtained in samples incubated with 5 x 10(-5) M SAMe. In aortic rings, lipid peroxidase production was inhibited in a concentration-dependent manner in the SAMe range of 10(-7) to 10(-5) M. Maximum inhibition (75.3 +/- 6.2%) was obtained with SAMe at 1.5 x 10(-5) M. Vascular 6-keto-PGF1alpha production showed a significant inverse linear correlation with vascular lipid peroxide production (Y = -0.04x + 18.1, r = 0.7309, P < 0.0001).