Unresponsiveness of forearm hemodynamics to omega-3 polyunsaturated fatty acids and aspirin

Prostaglandin synthesis has been reported to change with aspirin ingestion via cyclooxygenase enzyme inhibition and with marine oil supplementation via an increase in the metabolism of 3-series eicosanoids. This study investigated the effects of pharmacological manipulations of prostaglandin metabolism on forearm hemodynamics and blood pressure. The agents studied were omega-3 fatty acids and aspirin. In the omega-3 fatty acid study, two groups of normal volunteers (N = 10/group) supplemented their diets with either marine oil capsules or placebo. Hemodynamic variables (Mercury-in-Silastic forearm plethysmography) were measured initially and weekly for 4 weeks. There were no significant differences between the two groups in blood pressure, forearm blood flow, venous capacitance, or forearm vascular resistance. Parallel changes occurred for forearm blood flow and venous capacitance. Six normal volunteers took daily dosages of aspirin, increasing from 162 to 2600 mg. Hemodynamic measurements, ADP-induced platelet aggregation, and serum salicylate levels were obtained daily. Maximum inhibition of platelet aggregation occurred after 162 mg. (serum salicylate = 17.7 +/- 6.4 mg/l). Though serum salicylate levels rose to 165.0 +/- 20.0 mg/l, no significant changes occurred in blood pressure or forearm blood flow. Even at aspirin levels 16-fold greater than those required to impair platelet aggregation, the changes in forearm vascular resistance were not found to be significant. These results suggest that under resting conditions in normotensive males, neither pharmacological inhibition nor stimulation of vascular prostaglandin metabolism alters forearm vascular resistance or arterial blood pressure.