Tolerance to nitroglycerin is caused by reduced guanylate cyclase activation.
Since the diminished vasodilatation characterizing tolerance to organic nitrates is associated with lower rises in 3', 5'-cyclic guanosine monophosphate (cGMP) levels, the possibility that nitrovasodilators desensitized guanylate cyclase (GC) when pre-incubated with coronary supernatants was studied. In the absence of cysteine, pre-incubation with nitroglycerin (NG) decreased GC-activity during subsequent incubation to 24 +/- 7% of control values, whereas six other nitrovasodilators had much smaller effects. When cysteine was present during pre-incubation, NG-stimulation of GC remained significantly higher (59 +/- 3%; P less than 0.05), whereas the effects of other nitrovasodilators were not significantly changed. We also found that GC-activity, when reduced by pre-incubation with NG could only be restored by readdition of native coronary supernatant, suggesting that the enzyme became inactivated. NG pre-incubation of GC (in contrast to coronary strips) almost completely abolished the direct and thiol-independent stimulatory effect of 3-morpholinosydnonimine (SIN-1) down to 4.5 +/- 0.2%, whereas pre-incubation with other nitrovasodilators reduced the stimulatory response to SIN-1 to only 59 to 98%. Increasing concentrations of NG during pre-incubation dose-dependently (IC50 = 0.13 mM) reduced the activating effect of SIN-1 during incubation. There was also a time dependence in NG-induced inactivation of GC which followed first order kinetics with a calculated half life of 2.5 min in the absence of a thiol. The latter was increased to 4.0 or 19.2 min, respectively, when glutathione or cysteine-methylester were present during pre-incubation.(ABSTRACT TRUNCATED AT 250 WORDS)
Romanin
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C
Institute of Pharmacodynamics and Toxicology, University of Graz, Austria.
Kukovetz
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WR
D000818:Animals; D002417:Cattle; D003331:Coronary Vessels / Q000187:drug effects / Q000201:enzymology; D003545:Cysteine / Q000494:pharmacology; D004361:Drug Tolerance; D004789:Enzyme Activation / Q000187:drug effects; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008981:Molsidomine / Q000031:analogs & derivatives / Q000494:pharmacology; D005996:Nitroglycerin / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology
D014665:Vasodilator Agents; C002385:linsidomine; D008981:Molsidomine; D006162:Guanylate Cyclase; D005996:Nitroglycerin; D003545:Cysteine