Selective nitration of prostacyclin synthase and defective vasorelaxation in atherosclerotic bovine coronary arteries

Prostacyclin synthase (PCS) is an enzyme with antithrombotic, antiprolifera tive, and dilatory functions in the normal vasculature, and inactivation of PCS by tyrosine nitration may favor atherosclerotic processes. Here, we sh ow that PCS is nitrated and inactivated in early stage atherosclerotic lesi ons (focal intimal thickenings). Immunoprecipitation with antibodies raised against nitrotyrosine yielded PCS as the main nitrated protein in blood ve ssels. Moreover, we identified two nitrated degradation products of PCS wit h molecular mass of 30 and 46 kd, which were selective for atherosclerotic tissue. Agonist (acetylcholine, angiotensin II)-induced prostacyclin format ion was decreased in atherosclerotic vessels compared with normal tissue, w hereas PGE(2) formation was increased and cyclooxygenase activity remained unchanged. A selective loss of PCS activity was confirmed by direct measure ment of enzymatic activity. In line with this, we observed defective relaxa tion of early atherosclerotic vessels following vasoconstrictive stimulatio n, This functional impairment was completely reversed by coincubation with an antagonist of the thromboxane/PGH(2) receptor but not by a thromboxane s ynthase inhibitor. These data suggest that reduced PCS activity in atherosc lerotic arteries prevents the rapid use of PGH(2), which accumulates and ac ts as an agonist on the vasoconstrictive thromboxane receptor.