Failure of nifedipine and reperfusion to reduce infarct size relative to region at risk as measured by NADH fluorophotography

Benidipine Reduces Myocardial Infarct Size Involving Reduction of Hydroxyl Radicals and Production of Protein Kinase C-Dependent Nitric Oxide in Rabbits

Japanese white rabbits underwent 30 minutes of ischemia and 48 hours of reperfusion. Benidipine (3 or 10 microg/kg, i.v.) was administered 10 minutes before ischemia with and without pretreatment with L-NAME (10 mg/kg, i.v., a NOS inhibitor), chelerythrine (5 mg/kg, i.v., a PKC blocker) or 5-HD (5 mg/kg, i.v. a mitochondrial KATP channel blocker), genistein (5 mg/kg, i.v. a protein tyrosin kinase blocker). SNAP (2.5 mg/kg/min x 70 minutes, i.v., an NO donor) was also administered 10 minutes before ischemia. Benidipine significantly reduced the infarct size in a dose-dependent manner (3 microg/kg: 29.0 +/- 2.7%, n = 8, 10 microg/kg: 23.0 +/- 2.4%, n = 10) compared with the control (41.6 +/- 3.3%, n = 10). This effect was completely blocked by L-NAME (39.9 +/- 3.6%, n = 8) and chelerythrine (35.5 +/- 2.4%, n = 8) but not by 5-HD (23.0 +/- 2.4%, n = 10) or genistein (24.6 +/- 3.1%, n = 10). SNAP also reduced the infarct size (24.6 +/- 3.1%, n = 8). Benidipine significantly increased the expression of eNOS mRNA at 30 minutes after reperfusion and significantly increased the expression of eNOS protein at 3 hours after reperfusion in the ischemic area of the left ventricle. Benidipine and SNAP significantly decreased myocardial interstitial 2,5-DHBA levels, an indicator of hydroxyl radicals, during ischemia and reperfusion. Benidipine increased myocardial interstitial NOx levels, which effect was blocked by chelerythrine, during 0 to 30 minutes and 150 to 180 minutes after reperfusion. Benidipine reduces the infarct size through PKC-dependent production of nitric oxide and decreasing hydroxyl radicals but not through involving protein tyrosine kinase or mitochondrial KATP channels in rabbits.

Real time micro-fiberoptic monitoring of endogenous fluorescence in the rat conceptus during hypoxia

A micro-fiberoptic methodology has been developed for non-invasive, real time measurement of endogenous pyridine nucleotide fluorescence from the surface of the visceral yolk sac (VYS) in intact, viable rat conceptuses. Gestational day (GD) 10-12 conceptuses are maintained in a customized perifusion system, which allows for control of oxygenation, as well as the continuous measurement of pH and oxygen concentration in the effluent perifusate. Miniaturized light guides were constructed by drawing 250 microns ESKA acrylic optical fibers through a stainless steel sheath with a high strength epoxy polymer. A single fiber supplied the excitation signal from a mercury arc lamp at a wavelength of 366 nm. The emission signal was returned via three additional fibers, electronically amplified, processed, and recorded, using a dual channel lamp-compensated fluorometer, optimized for detection of reduced pyridine nucleotides at 455 nm. Endogenous fluorescence in the conceptus was monitored by placing the polished tip of the sensor directly on the surface of the VYS. Oxygen-equilibrated conceptuses, exposed to 100% nitrogen, produced a reproducible biphasic surface fluorescence peak, which returned to baseline levels upon reoxygenation of the perifusate. This biphasic response consisted of an initial rapid rise in fluorescence (phase I), followed by an attenuated rate in fluorescence signal increase (phase II). The hypoxia produced age-dependent rates of fluorescence change during phase I, while phase II remained relatively unchanged throughout GD 10-12. These results demonstrate the ability to monitor endogenous fluorescence, non-invasively and in real time, during the period of organogenesis in the intact rat conceptus and will provide valuable information in studies of embryonic metabolism and response to chemical embryotoxicants.

Rapid expression of heat shock protein in the rabbit after brief cardiac ischemia

The effect of brief myocardial ischemia on the expression of heat shock protein (HSP 70) was examined in an in vivo rabbit model of myocardial ischemia using Northern blotting. Functional studies were carried out in the open-chested anesthetized rabbit. The large marginal branch of the left circumflex was occluded four times for 5 min. Using piezoelectric crystals implanted midwall in the ischemic zone, end-diastolic length, end-systolic length, and percent segmental shortening were assessed. Expression of HSP 70 was measured by Northern blotting. A single 5-min coronary occlusion doubled the expression of HSP 70 whereas four cycles of 5 min of ischemia/5 min of reperfusion resulted in a threefold increase in HSP 70 mRNA (P less than 0.001). Measurements with the piezoelectric crystals showed mild myocardial dysfunction concomitant with the increase in HSP 70. This increase in HSP 70 mRNA after repetitive brief ischemia was transient, occurring as early as 1 h and returning to baseline by 24 h after ischemia. Western blot analysis with a monoclonal antibody to HSP 70 was used to compare sham and postischemic myocardial HSP 70 levels. Changes in the amount of HSP 70 were evident as early as 2 h and were even more striking at 24 h.

The detection of technical failures in perfused heart with ischemia and reperfusion by epicardial NADH fluorescence

This study documents the value of continuous observation of nicotinamide adenine dinucleotide (NADH) fluorescence (NADH-F). NADH-F monitoring is used to identify ischemic regions for the recognition of minor technical failures associated with ischemia and reperfusion experiments in the isolated perfused heart system. The visualization of NADH-F is possible by simply irradiating the heart with ultraviolet light. Rat hearts, in the working-heart mode, were subjected to occlusion/reperfusion of the left coronary artery, and analyzed. The perfusate was filtered through a 5 micron pore membrane. Out of 281 hearts which were judged to be free of technical failures by conventional physiological indices (heart rate greater than 200/min, cardiac output greater than 34 ml/min, and coronary flow 9-14 ml/min), 43 (15%) disclosed an abnormal NADH-F area prior to the coronary intervention. During coronary intervention, 29 technical failures were detected as indicated by sparse NADH-F distribution with occlusion, delayed disappearance of NADH-F upon reperfusion, or the exhibition of an abnormal NADH-F region unassociated with the coronary artery supply area. These technical failures are not detectable without the use of NADH-F, although the actual number of failures detected may depend on the skill of the operator. We recommend NADH-F monitoring for any preparations which do not contain hemoglobin, since NADH-F is an intrinsic probe for ischemia and is easily applicable to a variety of experiments.

Effect of amlodipine on myocardial functional and metabolic recovery following coronary occlusion and reperfusion in dogs

The effects of the dihydropyridine calcium-channel blocker, amlodipine, on subendocardial segment shortening (%SS), regional myocardial blood flow, myocardial high-energy phosphate levels and tissue water content were compared to those of a saline-treated group of barbital-anesthetized dogs subjected to a 45-minute coronary artery occlusion followed by 60 minutes of reperfusion. Saline or amlodipine (200 micrograms/kg, IV) were administered 15 minutes prior to coronary occlusion. There were no significant differences between groups in ischemic bed size or hemodynamics, although dP/dt was higher following amlodipine. Subepicardial collateral blood flow was higher in the amlodipine group during coronary occlusion. Following occlusion, %SS in the ischemic region was markedly decreased in both series and passive systolic lengthening resulted. In spite of similar decreases in %SS during occlusion, the amlodipine- treated dogs showed a marked improvement in myocardial segment function (%SS) of the ischemic-reperfused region throughout 60 minutes of reperfusion as compared to saline-treated animals. In addition, amlodipine prevented the rebound increase in phosphocreatine and attenuated the loss of adenine nucleotides and the increase in tissue water in the ischemic-reperfused area at 60 minutes of reperfusion. These results suggest that amlodipine has a favorable effect on the functional and metabolic recovery of the ischemic-reperfused myocardium, and may have potential as a therapeutic agent for the treatment of coronary artery disease. The mechanism of action of amlodipine in this model is unknown but may be partially related to a drug-induced increase in coronary collateral blood flow.

Calcium antagonists and the ischemic myocardium

Recent laboratory studies have shown that the calcium antagonists (slow channel blockers) can protect the myocardium against the consequences of experimentally induced ischemia and reperfusion. With one recent exception, however, clinical trials relating to the effectiveness of these drugs in the management of patients with myocardial infarction have been disappointing. This paper explores this apparent discrepancy.

Effects of calcium antagonists on infarcting myocardium

Numerous studies have been conducted over the past 10 years on the effects of calcium antagonists on regional myocardial ischemia and infarct size. Verapamil, for example, reduced the degree of adenosine triphosphate degradation during 15 minutes of coronary occlusion followed by reperfusion in an anesthetized canine preparation. It also preserved the ultrastructural appearance of mitochondria in myocardium subjected to 1 hour of ischemia. Using an 8-hour permanent coronary artery occlusion model in which risk zone was assessed with radioactive microspheres and infarct size determined by tetrazolium staining, verapamil, administered 1 hour after occlusion, resulted in a modest decrease in infarct size. In a reperfusion model in which anesthetized dogs were subjected to 3 hours of coronary artery occlusion followed by 3 hours of reperfusion, verapamil decreased infarct size when it was administered during the period of ischemia, but failed to decrease infarct size when administered only during the reperfusion phase, i.e., after 3 hours of ischemia. Although verapamil is known to have negative inotropic effects, the newer calcium antagonist agent nisoldipine is less negatively inotropic, and might therefore be preferable in the situation of compromised hemodynamics. In a 6-hour permanent coronary artery occlusion model, nisoldipine decreased infarct size without decreasing left ventricular contractility. Most published reports support the concept that calcium antagonists decrease infarct size in models of experimental infarction. Of 4 major clinical studies, only 1 has shown that calcium antagonists are capable of reducing infarct size in man. However, in most of these studies, drug therapy commenced relatively late--4 or more hours after symptoms. In order for these drugs to demonstrate beneficial effects, the risk zone may have to be small and the degree of collateral flow adequate, the drug may have to be given very early or even before coronary occlusion (in a prophylactic fashion) and administration of the drug may have to be coupled to early coronary reperfusion.

NADH in situ laser fluorimetry: effect of pentobarbital on continuously monitored myocardial redox state

NADH laser fluorimetry was applied to in situ monitoring of pentobarbital overload effect on myocardial redox state in rats. Experiments were carried out on open-chest rats anesthetized with pentobarbital. Use of very thin optical probes allowed measurements of NADH fluorescence directly within the myocardial wall. Quantitative analysis of fluorescent and backscattered light signals was made possible on-line. In 8 animals, a slow IV infusion of 6% pentobarbital (2 mg.min-1 for 10 min) induced an average twofold increase in NADH fluorescence, with constant return to baseline level prior to injection after a maximum period of 50 min. Thus, pentobarbital overload strongly affects the myocardial energetic state, and this effect was precisely evaluated with NADH fluorescence monitoring. In situ-monitored myocardial redox state variations during pentobarbital infusion can constitute a reference for similar studies on pharmacological agents aimed at protecting tissues against ischemic biochemical damages.