A direct protective effect of sulphinpyrazone on ischaemic and reperfused rat hearts

Mechanisms of protection afforded by cyclooxygenase inhibitors to endothelial function against ischemic injury in rat isolated hearts

The aim of this study was to assess whether cyclooxygenase (COX) inhibitors protect the endothelial function against the deleterious effect of ischemia and reperfusion. Isolated rat hearts perfused under constant-flow conditions were exposed to 30 min of partial ischemia (flow, 1 ml/min) followed by 20 min of reperfusion, after which coronaries were precontracted with U-46619, and the response to the endothelium-dependent vasodilator, serotonin (5-HT), was compared with that of the endothelium-independent vasodilator, sodium nitroprusside (SNP). In untreated hearts, ischemia diminished selectively 5-HT-induced vasodilation, compared with sham hearts (without ischemia). The vasodilation to SNP was unaffected in all groups. Pretreatment with 6-MNA, 30 microM, a COX-2 inhibitor with some activity on COX 1, diclofenac, 1 microM (COX-1 and -2), or 1-(7-carboxyheptyl) imidazole, 10 microM [thromboxane (TX) synthase inhibitor] but not indomethacin, 10 microM (COX-1 inhibitor) preserved the vasodilation induced by 5-HT after ischemia. Enzyme immunoassays indicated that all COX inhibitors decreased the concentration of TXB2 and 6-keto-PGF1alpha [stable metabolites of TXA2 and prostacyclin (PGI2), respectively] in coronary effluent during ischemia. Furthermore, indomethacin was the only one to abolish the concentration of PGE2 during ischemia and early reperfusion. No clear trend on ventricular postischemic recovery could be observed between treated and untreated groups under our experimental protocols. These data suggest that, under our conditions, 6-MNA, diclofenac, and 1-7-CHI, but not indomethacin, protect the endothelial function via a reduction in TX concentration. Disparities between COX inhibitors may be due to the complete abolition of PGE2 concentration during ischemia and reperfusion in the indomethacin group.

Sulfinpyrazone prolongs survival and decreases platelet uptake of heart allografts

The purpose of this study was to evaluate the potential benefit of the platelet active drug sulfinpyrazone (SPZ) on uptake of indium-III-oxine (111In)-labeled platelets and survival of rat heart allografts. Lewis rats bearing ACI heterotopic heart transplants were treated with SPZ in high, intermediate, or low doses. In 111-labeled platelet uptake was measured 5 days postoperatively and calculated as a ratio between the transplanted and native hearts. Left and right ventricles were measured separately. SPZ given in doses of 400 and 200 mg/kg daily significantly decreased platelet uptake in the graft and reduced the ratio of uptake between transplanted and native hearts (P less than 0.05). In animals treated with SPZ 100 mg/kg/day platelet uptake was not significantly less than that of the nontreated control animals. Survival of allografts was determined by daily palpation and compared to vehicle-treated controls. Mean graft survival was prolonged for animals treated with 100 mg/kg and 200 mg/kg daily, i.e., 19.0 +/- 3.02 and 11.42 +/- 1.97 days, respectively. Animals administered 400 mg/kg did not have longer graft survival than controls (6.63 +/- 0.66 versus 6.31 +/- 0.18 days). Most animals in the 400 mg/kg group died as a result of adverse side effects of the drug. We conclude that SPZ in low to intermediate doses prolongs allografted heart survival. The enhanced survival in the lower dose group may in part be due to mechanisms other than platelet adhesiveness.

The amplified chemiluminescence test to characterize antirheumatic drugs as oxygen radical scavengers

High levels of reactive oxygen species (ROS) are generated by phagocytes involved in host defence and inflammation. Thus, it appears highly desirable to learn more about the potential of antirheumatic drugs to scavenge ROS or to inhibit their enzymatic generation. Amplified chemiluminescence (CL) allows detection of O-2 using lucigenin (LgCL) or H2O2 using luminol (LuCL). A total of 43 compounds have been tested quantitatively in vitro (10(-6) to 10(-4) mol/l) with respect to three test parameters; varying cell-activity, and incubation-time employing two different phagocyte populations (neutrophils/macrophages). The most active compounds with LgCL were the known radical scavengers nordihydroguaiaretic acid (NDGA), N-propyl gallate, superoxide dismutase and chloroquine, the non-steroidal anti-inflammatory drugs (NSAID) benzydamine, timegadine, carprofen, enolicam, the known lipoxygenase inhibitors (e.g. CBS 1108/1114, BW 755C) and glucosaminoglucan polysulfate. Inactive in this system were corticosteroids (prednisolone, dexamethasone) most of the tested NSAID (N = 16/20), most disease modifying drugs (D-penicillamine, levamisole, gold-TM) and the anti-gout drugs (sulfinpyrazone, allopurinol, colchicine). Therefore amplified CL with lucigenin appears to be a rapid, kinetic, reproducible means of pharmacological profiling in vitro new anti-inflammatory drugs for radical scavenger activity.

Electrical changes produced by injury to the rat myocardium in vitro and the protective effects of certain antiarrhythmic drugs

Glass microelectrodes were used to record intracellular electrical activity from rat isolated and superfused atrial myocardium during external electrical stimulation. After 2 h in normal oxygenated physiological salt solution the muscle was exposed for 30 min to a superfusate simulating the composition of extracellular fluid during myocardial ischaemia (SI). This fluid contained lactate (20 mM), a raised potassium concentration (7 mM), no glucose and a pH lowered to 6.4, and was gassed with N2 in place of O2 (hypoxia). During SI the diastolic threshold voltage for stimulation increased, the speed of action potential conduction between the right and left atria slowed, and both the effective and functional refractory periods of the right atrium shortened, as did the duration of the right atrial action potential. The only component of SI which separately caused electrical changes similar to those of the full simulation was hypoxia. Addition to the superfusate of verapamil (0.5 micrograms ml-1), sulphinpyrazone (1-20 micrograms ml-1) or indomethacin (10-20 micrograms ml-1) attenuated many of the SI-induced electrical changes, although indomethacin was much less effective than the other two drugs. Lowering the calcium concentration of the superfusate from 2 mM to 0.5 mM protected against the SI-induced electrical changes that were inhibitable with sulphinpyrazone and verapamil.

A protective effect of sulphinpyrazone against coronary occlusion-induced shortening of myocardial refractory periods in the rat

The hearts of anaesthetized, artificially ventilated rats were exposed, and the left coronary artery occluded. The diastolic threshold voltage for stimulation (DTV), the duration of the bipolar electrogram (DBE) and the functional refractory period (FRP) of the ischaemic area were measured at minute intervals for an hour after occlusion. Coronary occlusion caused a rise in DTV, a prolongation of the DBE and a biphasic change in the FRP, with an initial prolongation phase (1-4 min) followed by a decline to below pre-occlusion values (5-15 min). Episodes of ventricular tachyarrhythmia (VT) were most frequent during the period 5-15 min after the onset of occlusion of the coronary artery. This coincided with the period when FRP was minimal and the difference between DBE and FRP was maximal. Pretreatment of rats with sulphinpyrazone (2.5-40 mg kg-1) or indomethacin (5-20 mg kg-1) protected against the episodes of coronary occlusion-induced VT and against the associated decline in FRP of the ischaemic muscle. Sulphinpyrazone was more effective than indomethacin in this respect and a combination of the two drugs was approximately as effective as sulphinpyrazone alone. It was concluded that sulphinpyrazone protects rats against coronary occlusion-induced episodes of VT by reducing the risk of ventricular action potential re-entry. This effect is probably due to protection against the ischaemia-induced shortening of the myocardial FRP.

Toxic properties of arachidonic acid on normal, ischemic and reperfused hearts. Indirect evidence for free radical involvement

We studied the effect of arachidonic acid on function and CPK release of normal, ischemic and reperfused isolated rat hearts. Under control conditions arachidonate (10 micrograms/ml) produced a transient inotropic effect which gradually reversed during a 90 minute perfusion. Creatinephosphokinase (CPK) release was augmented by arachidonic acid, particularly under high flow (pre-ischemia and reperfusion) conditions. Recovery of contractility following reperfusion of ischemic myocardium was significantly depressed by arachidonic acid. Vitamin E (100 ng/ml) an antioxidant and free radical scavenger, reduced the enzyme leakage and enhanced recovery of contractility of reperfused myocardium. It also prevented the depression in contractility during control perfusion. Similar protective effects were observed by perfusing the heart with reduced calcium but not by nifedipine; a calcium channel blocker, indomethacin; a prostaglandin synthesis inhibitor or nordihydroguarietic acid; a lipoxygenase inhibitor. Arachidonic acid also inhibited membrane Na+/K+-ATPase although it is unlikely that this property mediated its cardiotoxic influence since it was not prevented by vitamin E. In addition, we observed that arachidonic acid increased the coronary resistance of isolated hearts, probably through enhanced calcium influx as this constriction was reduced by low calcium as well as by nifedipine. Thus, arachidonic acid possesses distinct properties. Its cardiotoxic influence is likely mediated by free radical generation.