TOLERANCE TO NITROGLYCERIN IN VASCULAR SMOOTH-MUSCLE CELLS IS NOT AFFECTED BY THE LEVEL OF INTRACELLULAR GLUTATHIONE OR L-CYSTEINE

A major hypothesis for the mechanism of tolerance to nitroglycerin (NT G) is that continued use causes a decrease in thiol donors within the vascular smooth muscle cell that are essential for the effect of NTG. We tested this idea directly in the target cell. NTG tolerance, measur ed as reduced formation of intracellular cyclic guanosine monophosphat e (cGMP), was induced in pig coronary smooth muscle cells. The consequ ence of altering intracellular levels of the thiol donors, glutathione (GSH) and L-cysteine (L-cys), was determined. Incubating cells with 1 00 mu M NTG for 1 h caused an 83% reduction in cGMP formation in respo nse to acute readministration of 200 mu M NTG for 2 min but was not as sociated with a reduction in intracellular GSH or L-cys. This result w as not altered when intracellular GSH levels were increased threefold by including 1 mM GSH in the incubation buffer. Also, recovery from to lerance was not affected by supplementation with GSH. Further, the res ponse of cGMP to NTG was not altered by inhibiting the synthesis of GS H and lowering intracellular levels of GSH by 77%. Similar findings we re made with supplemental L-cys or N-acetyl-L-cysteine. These results do not support the hypothesis that tolerance to NTG is the result of a reduction of the thiol donors GSH and L-cys within vascular smooth mu scle cells.