Response to changing plasma concentrations of isosorbide-bound NO2 during acute and sustained treatment with isosorbide dinitrate in patients with coronary artery disease

Background: The mechanisms behind development of tolerance to nitrate effec ts during sustained, asymmetric isosorbide dinitrate (ISDN) therapy are not fully understood. Hypothesis: The study was undertaken to investigate the changes of the rela tionships between left ventricular (LV) function and plasma concentrations of ISDN and its vasoactive metabolites (2- and 5-ISMO) during acute and sus tained, asymmetric ISDN therapy. Methods: Left ventricular function and plasma concentrations of ISDN, 2- an d 5-isosorbide mononitrates (P-ISDN, P-2-and 5-ISMO) were measured at rest and at supine exercise before and for 4 h after peroral 30 mg ISDN in 15 pa tients with coronary artery disease, all with initial exercise pulmonary ar tery wedge pressure (PAWP) >25 mmHg. Seven patients were untreated (acute g roup), while eight received 30 mg ISDN b.i.d. for 2 weeks before the invasi ve study. P-ISDN and the concentration of available isosorbide-bound nitrat e (NO2) in plasma (P-ISDN.2 + P-2-ISMO + P-5-ISMO) (P-NO2) were used as mea sures of the nitric oxide (NO) offer to the tissues. Results: Throughout the study, after administration of medication, all plas ma concentrations, in particular P-ISDN, were higher in the chronic than in the acute group. Peak P-ISDN was reached after 15 min in the chronic group and after 25 min in the acute group, while P-2- and 5-ISMO reached maximum only after 40 min in both groups. At rest, the full effect on PAWP was obs erved after 10 min in both groups, but at markedly higher levels of P-ISDN and P-NO2 in the chronic group. Afterward, no further changes in PAWP were observed. During exercise, 1 h after medication, PAWP and stroke index to P AWP ratio (SI/PAWP) were normal in both groups. Thereafter, at slowly decli ning P-NO2, PAWP rose and SI/PAWP declined toward the initial level in the chronic group, but remained unchanged in the acute group, in spite of highe r P-NO2 and greater NO release in the former. Conclusions: Patients receiving sustained, asymmetric 30 mg ISDN b.i.d. dos ing had the same immediate beneficial effects on LV function during exercis e after a morning dose as did untreated patients. However, in spite of high er P-NO2 and higher rate of NO release during sustained treatment, the effe cts deteriorated gradually 2 to 3 h after medication. The changes in metabo lism and/or distribution of isosorbide-bound NO2 may possibly be part of th e tolerance induced by long-term treatment, even with asymmetric dosing.