TOLERANCE TO SODIUM-NITROPRUSSIDE - STUDIES IN CULTURED PORCINE VASCULAR SMOOTH-MUSCLE CELLS

Background: Tolerance to nitrovasodilators, including sodium nitroprus side (SNP), is a clinical problem. SNP causes vasodilatation by releas ing nitric oxide, which stimulates intracellular guanosine 3':5'-cycli c monophosphate (cGMP) accumulation in smooth muscle cells. This study examined tolerance to SNP in coronary smooth muscle cells by measurin g intracellular cGMP formation. Methods. Smooth muscle cells were isol ated from pig coronary vessels. Intracellular cGMP formation in respon se to SNP, nitroglycerine, and atrial natriuretic peptide (ANP) was qu antitated by radioimmunoassay before and after chronic pretreatment. R esults: The detection of tolerance of cells rechallenged with SNP requ ired exposure to a minimum concentration of 1 mum for SNP for at least 60 min. In untreated cells, acutely applied 100 mum SNP increased the cGMP concentration to 300 +/- 8.6 pmol/mg protein (mean +/- SEM). The cGMP concentration in cells pretreated with 1 mum SNP for 60 min incr eased to 213 +/- 11 pmol/mg in response to 100 muM SNP (P < 0.01, comp ared to untreated cells). The pretreatment of cells for 60 min with in creasing concentrations of SNP caused a sequential reduction in the ac ute concentration-response curves of cGMP to SNP. After a 6 h washout period, cGMP accumulation in response to a rechallenge with SNP return ed to control levels. The acute concentration-response curve of vGMP t o SNP in cells pretreated with 100 muM nitroglycerine for 60 min was r educed significantly. Pretreatment with 100 mum SNP for 60 min did not change the response of cAMP accumulation to isoproterenol or forskoli n. However, the response of cGMP formation to ANP was potentiated afte r pretreatment. In addition, elevation of basal cAMP or cGMP concentra tions, induced with isoproterenol or ANP, respectively, did not alter the response of cGMP formation to SNP. Conclusion: The study yielded t he following findings: (1) reversible tolerance to SNP was induced in cultured vascular smooth muscle cells; (2) chronic exposure to nitrogl ycerine induced cross-tolerance to SNP; (3) cells that were tolerant t o SNP showed a potentiated response to ANP.