Endothelial dysfunction occurs in the presence of active endothelial nitric oxide synthase

Impaired vascular reactivity occurs in postischemic hearts with marked reduction in endothelium-dependent relaxation (EDR). However, it is unknown if this effect requires loss of endothelial nitric oxide synthase (eNOS) or simply impaired signal transduction. This study evaluated the correlation between abolishment of EDR and eNOS activity Isolated rat hearts (n=21) were perfused at constant flow and endothelial reactivity assessed with histamine (10^-5M) and calcium ionophore (1μM) Hearts were then bolused with 0.12cc of Triton X-100 (TX) and retested for vasodilators response. Direct measurements of NO formation were performed by electron paramagnetic resonance (EPR) spectrometry in the coronary effluent of the hearts eNOS activity was assayed in control and TX-treated hearts using the ¹⁴C-argininc to ¹⁴C-citrulline method. Western blot (WB) and immunoelectron microscopy. (IEM) were also performed in these hearts to determine the amounts of the enzyme Hearts initially exhibited reduction of coronary pressure upon infusion of histamine (18±4mmHg) and calcium ionophore (16±2mmHg) which was totally abolished after treatment with TX. While a typical triplet EPR signal was detected in control hearts, no signal was seen after TX injection. eNOS activity measurements of TX hearts showed no significant change when compared to control (0.61±0.02 vs. 0.58±0.01 pmoles/min x mg, p=NS). Similarly, 135kDa bands of equal intensity were observed in WB studies before and after TX treatment. IEM revealed identical labeling of the EC membranes despite discrete disruption after TX treatment. Therefore, mild detergent treatment with TX caused loss of EDR and NO in the presence of active eNOS suggesting depletion of substrate/cofactors.