Release of proinflammatory and prothrombotic mediators in the brain and peripheral circulation in spontaneously hypertensive and normotensive wistar-kyoto rats

Background and Purpose: We reported previously that stroke risk factors prepared the brain stem for the development of ischemia and hemorrhage and induced the production of tumor necrosis factor following an intrathecal injection of lipopolysaccharide, a prototypic monocyte-activating stimulus. This study evaluates whether blood or brain cells of hypertensive rats produce more proinflammatory and prothrombotic mediators than do blood or brain cells of normotensive rats. Methods: Levels of tumor necrosis factor, platelet-activating factor, 6-ketoprostaglandin F_1a, and thromboxane B₂ in the cerebrospinal fluid and blood of spontaneously hypertensive and normotensive Wistar-Kyoto rats were monitored before and after a challenge with lipopolysaccharide. Results: Little or no activity from these mediators was found in the cerebrospinal fluid or blood of saline-injected control animals. Intravenous administration of lipopolysaccharide (0.001, 0.1, and 1.8 mg/kg) produced dose-dependent increases in blood levels of all mediators in hypertensive rats. In normotensive rats the levels were less than in hypertensive rats and were not clearly dose-related. When lipopolysaccharide was injected intracerebroventricularly, more tumor necrosis factor was measured in the cerebrospinal fluid than in the blood, suggesting local synthesis of this cytokine. Levels of tumor necrosis factor and platelet-activating factor in the cerebrospinal fluid were higher in hypertensive than in normotensive rats. The thromboxane A₂/prostacyclin ratio was not altered significantly between the two rat strains. Conclusions: It is suggested that the higher incidence of brain stem ischemia and hemorrhage after the intrathecal injection of lipopolysaccharide in hypertensive rats than in normotensive rats might be related to the higher levels of the two cytotoxic factors tumor necrosis factor and platelet-activating factor produced in response to such challenge.