RESPONSE OF CULTURED CEREBRAL-ARTERY SMOOTH-MUSCLE CELLS TO THE NITRIC-OXIDE VASODILATORS, NITROGLYCERIN AND SODIUM-NITROPRUSSIDE

We characterized the response of soluble guanylyl cyclase in smooth mu scle cells cultured from cerebral vessels to the nitric oxide (NO)prod ucing vasodilators, nitroglycerin (NTG) and sodium nitroprusside (SNP) and determined the ability of these agents to induce tolerance. Smoot h muscle cells were isolated from porcine basilar, anterior and middle cerebral, and internal carotid arteries. Following an initial series of experiments using NTG at various concentrations and times of exposu re to determine conditions, concentration-response curves of intracell ular guanosine 3',5'-cyclic monophosphate (cGMP) to NTG and SNP were d etermined in cells pretreated for 1 h with 100 mu mol NTG to induce to lerance and compared with response curves in control cells. Basal cGMP levels were 2.1 +/- 0.4 pmol/mg cell protein (n = 16). Both NTG and S NP increased cGMP in nontolerant cells, and SNP was more effective. Ma ximum concentrations of SNP (1 mmol/L) increased cGMP to 163 +/- 5.9 p mol/mg versus 21 +/- 2.4 pmol/mg for 1 mmol/L NTG (p < 0.01). Cells ma de tolerant to NTG were unresponsive to NTG up to 1 mmol/L but remaine d responsive to SNP, However, the response curve to SNP was significan tly depressed by similar to 25%. Following washout of NTG in tolerant cells, the response of cGMP to SNP returned to control within 12 h, wh ile response to NTG required 36 h. Similar experiments were conducted in cells initially made tolerant to SNP. These results indicate that c erebral artery smooth muscle cells in culture express a functioning so luble guanylyl cyclase and the enzymes that are necessary to metaboliz e NTG to NO. Prolonged exposure of the cells to NTG induced tolerance as well as cross-tolerance to SNP.