SILICA ATTENUATES HYPERTENSION IN LYON HYPERTENSIVE RATS

Background and objective: Evidence has been provided suggesting an ass ociation between hypertension and immune dysfunction in Lyon hypertens ive (LH) rats. In the present study, we investigated the possible role played by macrophages in LH rats by examining the blood pressure cons equences of the chronic administration of silica, a selective toxin to macrophages in vivo. Design and methods: LH and Lyon low blood pressu re (LL) male rats were treated with silica at a dose of 200 mg/kg per week intraperitoneally from age 4-10 weeks. Controls received saline. Blood pressure was measured by plethysmography from age 6-10 weeks and an intra-arterial recording was performed in Ii-week-old, freely movi ng rats. Results: Treatment with silica did not modify blood pressure in LL rats at any age. In contrast, 1 week after the beginning of the treatment, the blood pressure of silica-treated LH rats was lower than that of untreated LH rats. As shown by intra-arterial recording, the effect persisted 1 week after cessation of the treatment. In addition, silica decreased the left ventricle weight in LH but not in LL rats. Conclusion: The present results show that weekly administration of sil ica in young LH rats attenuates the development of hypertension and of left ventricular hypertrophy, a finding which suggests that macrophag e-mediated immune reactions may play a pathogenic role in LH rats.