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C Szabo, JA Mitchell, SS Gross, C Thiemermann and JR Vane
William Harvey Research Institute, St. Bartholomew's Hospital Medical College, London, United Kingdom.
We investigated the effect of the calcium channel antagonist nifedipine on the induction of nitric oxide synthase (NOS) by bacterial endotoxin (lipopolysaccharide; LPS) in J774.2 macrophages, in cultured rat aortic smooth muscle cells and in a rat model of endotoxin shock. Stimulation by LPS for 24 hr increased nitrite accumulation in the supernatant of both cell types. NOS induction accounts for this nitrite accumulation, as both NG-methyl-L-arginine and cycloheximide reduced nitrite production in both cell types. Dexamethasone inhibited LPS-stimulated nitrite production in macrophages, but not in rat aortic smooth muscle cells. Nifedipine inhibited the production of nitrite in these LPS- treated cell types, with a more pronounced effect on macrophages. However, nifedipine did not inhibit the production of nitrite in J774.2 cells in which NOS had already been induced by prior exposure to LPS, and any possible further induction was inhibited by cycloheximide. In anesthetized rats subjected to LPS, pretreatment with nifedipine or dexamethasone ameliorated the fall in mean arterial blood pressure and the vascular hyporeactivity to norepinephrine at 180 min after LPS injection. At 180 min after LPS, an increase in a calcium-independent (induced) NOS activity was measured in lung homogenates. This induced NOS activity was reduced in lungs from rats treated with nifedipine or dexamethasone before LPS. Thus, nifedipine inhibits the induction of NOS in response to LPS in cultured cells in vitro and in the anesthetized rat.
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