Role of nitric oxide in regulation of coronary blood flow during myocardial ischemia in dogs

Objectives. This study was undertaken to examine whether nitric oxide released in ischemic myocardium decreases the coronary vascular resistance and attenuates the severity of contractile and metabolic dysfunction.Background. Endothelium-derived relaxing factor, recently identified as nitric oxide, is a potent relaxant of coronary smooth muscle.Methods. The left anrterior descending coronary artery was perfused through an extracorporeal bypass tube placed in the carotid artery in 56 open chest dogs. After hemodynamic stabilization, we occluded this bypass tube to decrease coronary blood flow to one third of the control flow. Thereafter, we maintained a constant coronary perfusion pressure(40.9 ± 3.1mm Hg).Results. Under ischemic conditions, the coronary arteriovenous differences in nitrate and nitrite (end products of nitric oxide) increased (from 3.5 ± 0.4 [mean ± SEM] to 12.9 ± 2.1 μmol/liter, p < 0.01). ⁰-Monomethyl -arginine (3 μg/kg body weight per min, intracoronary) decreased the coronary arteriovenous differences in nitrate and nitrite (5.0 ± 0.9 μmol/liter, p < 0.05) and coronary blood flow (from 29.8 ± 0.5 to 18.1 ± 1.1 ml/100 g per min, p < 0.001). Fractional shortening (from 3.7 ± 1.0 to −1.3 ± 0.7%, p < 0.001) and lactate extraction ration (from −44.0 ± 4.1 to −59.2 ± 4.9%, p < 0.005) of the perfused area also decreased. These values were restored by the concomitant administration of -arginine. Blood flow to the endomyocardium was decreased relative to the epimyocardium. A reduction in coronary blood flow and worsening of myocardial contractile and metabolic functions due to the administration of ^G-monomethyl -arginine during ischemia were observed in denervated hearts. A reduction in coronary blood flow in ischemic myocardium was observed with the administration of ^W-nitro- -arginene methyl ester as well, although neither ^W-nitro- -arginine methyl ester nor ^G-monomethyl -arginine changed coronary blood flow and myocardial contractile and metabolic functions in the nonischemic myocardium. The cyclic guanosine monophosphate content of epicardial coronary artery increased due to myocardial ischemia; this increased was attenuated with ^G-monomethyl -arginine treatment.Conclusions. We conclude that endogenous nitric oxide predominantly decreases the coronary vascular resistance of ischemic endomyocardium, thereby improving myocardial contractility and metabolic function.     

Wallerian degeneration after cerebral infarction: evaluation with sequential MR imaging

The dynamic signal intensity changes at magnetic resonance (MR) imaging in active and chronic wallerian degeneration in the corticospinal tract were evaluated. Forty-three patients with wallerian degeneration seen on MR images after cerebral infarction were studied. When possible, patients with acute stroke were examined with MR imaging prospectively at the onset of symptoms and then at weekly intervals for several months. Focal infarction without distal axonal degeneration is demonstrated for the 1st month following onset of clinical symptoms. At 4 weeks, a well-defined band of hypointense signal appears on T2-weighted images in the topographic distribution of the corticospinal tract. After 10-14 weeks, the signal becomes permanently hyperintense. Over several years, accompanying ipsilateral brain stem shrinkage occurs. The dark signal intensity observed on T2-weighted images between 4 and 14 weeks is believed to result primarily from transitory increased lipid-protein ratio.     

Incompatibility of contrast agents with intravascular medications. Work in progress

In vitro and in vivo precipitation of iodinated contrast agents when ioxaglate and papaverine are given together has been reported. To verify these reports and to investigate other medications not previously tested, the authors analyzed mixtures of contrast agents and medications in vitro with a light spectrophotometer and observed them for visible precipitates for up to 120 minutes. Previously reported incompatibilities between ionic or low-osmolality contrast media and medications were verified, and several new incompatibilities were discovered. No incompatibilities were found when the drugs tested were mixed with the new nonionic contrast media.     

Influence of chlorhexidine and ethanol on the bond strength and durability of the adhesion of the fiber posts to root dentin using a total etching adhesive system

Introduction

The aim of this study was to investigate the effects of pretreatment of gel chlorhexidine (CHX) and ethanol (EtOH) on the bond strength and durability of the adhesion of the fiber post relined with resin composite to the root dentin using a total etch adhesive system.

Methods

Forty bovine incisor roots were divided into four groups after phosphoric acid etching: irrigation with physiologic solution (control), 5 minutes with CHX, 1 minute with EtOH, and 5 minutes with chlorhexidine followed by 1 minute with EtOH. Fiber posts relined with resin composite were cemented with either RelyX ARC (3M ESPE, St Paul, MN) and a total etch adhesive system Scotchbond Multi-Purpose (3M ESPE). Each group was randomly divided into two subgroups: 24 hours of storage and 12 months of storage. All roots were sectioned transversely, and the push-out test was performed. Failure modes were observed, and the bond strength means were analyzed by analysis of variance and the Tukey test (α = 0.05).

Results

CHX irrigation resulted in homogeneous bond strength values at 24 hours and 12 months of storage (P < .05). A significant bond strength decrease was noticed after 12 months of storage when irrigations were performed with physiologic solution and EtOH application only or associated with CHX (P < .05).

Conclusions

The use of CHX pretreatment could preserve the bond strength of the fiber post relined with resin composite to root dentin for 12 months. The use of EtOH and CHX followed by EtOH did not preserve the bond strength of the total etch adhesive system Scotchbond Multi-Purpose.