Direct effects of phosphamidon on isolated working rat heart electrical and mechanical function

QT Prolongation as an Isolated Long-Term Cardiac Manifestation of Dichlorvos Organophosphate Poisoning in Rats

Organophosphates (OP) are used extensively as pesticides and as chemical weapons. Cardiotoxicity is a major concern in survivors of the acute poisoning. To characterize the delayed cardiac effects of OP, rats were poisoned by intraperitoneal administration of dichlorvos. In group I, poisoning (0.25-, 0.75-, 1.4-LD₅₀) was followed by application of atropine and obidoxime. In group II, poisoning (0.35-, 0.5-LD₅₀) was done without antidotes. Cardiac evaluation included electrocardiography and echocardiography 2- and 6-week post-exposure, arrhythmia susceptibility following administration of Isoproterenol (150 mcg/kg), and histological evaluation. All poisoned animals displayed cholinergic symptoms. In group I, all animals exposed to 1.4-LD₅₀ (n = 3) had profound convulsions and died despite antidote treatment. However, in the lower doses, all animals survived and no cardiac abnormalities were noted during follow-up. In group II, six animals had convulsions and died. Surviving animals had mild but significant prolongation of corrected QT at both 2 and 6 weeks, compared to shams. There were no notable echocardiographic, gravimetric, or histological differences between poisoned and sham animals. Our data indicate that dichlorvos poisoning is associated with QT prolongation without anatomical or histopathological abnormalities. This new model can be used to elaborate the molecular mechanism\s of QT prolongation following OP poisoning.

Sociodemographic, clinical, and laboratory features of cases of organic phosphorus intoxication who attended the Emergency Department in the Southeast Anatolian Region of Turkey

In this study, sociodemographic, laboratory, and clinical features of cases of organic phosphorus (OP) intoxication in the Southeast Anatolian region of Turkey were investigated. Patients with OP intoxication admitted to the Emergency Service of Dicle University Hospital in Diyarbakyir City between May and August 1998 were evaluated. This prospective cohort study included five male (M) and 19 female (F) consecutive patients. Five cases were accidental intoxication; however, 19 cases were suicide attempts. Mean age of cases was 24+/-11 years; 54.2% of them were under the age of 20 years and 83.3% of them were under the age of 30 years. The M/F ratio was 1.0/3.8. The cases of suicidal purposeful intoxications were mostly determined in singles (58.3%, P<0.05). Most of the cases had a primary education level (16, 66.7%) and a lower socioeconomic status (14, 58.3%); 79.2% of cases admitted to our emergency service received atropine in primary health care centers. In emergency service, pralidoxime (PAM) was administered to only 29.2% of cases. According to ECG examination, tachycardia (14, 58.3%), ST changes (13, 54.2%), and T changes (3, 12.5%) were mostly seen; bradycardia and serious ventricular arrhythmias were not seen in any case. Patients who received atropine plus PAM had higher rates of arrhythmias, but this was not statistically significant (P>0.05). The most observed biochemical features of cases were leukocytosis (21 cases), hypokalemia (18 cases), and hyponatremia (4 cases). Other biochemical features were not evidently altered. In present cases, the most frequently seen symptoms and findings were vomiting (18, 75%), feeling faint (17, 70.8%), and tachycardia and dozing off (14, 58.3%). Serious ventricular arrhythmias were not observed, and in our region, OP intoxication especially affected young unmarried females, and most of them resulted from a suicidal purpose.

Obidoxime augments the positive inotropic effect of phosphamidon on the isolated working rat heart

The present study was designed to determine modulation of the direct inotropic effect of an anticholinesterase organophosphorus compound, phosphamidon, by the reactivator obidoxime. We investigated the effects of phosphamidon (n = 9), obidoxime (n = 5), and their combination (n = 5) on the mechanical and energetic indices of left ventricular function, in the isolated working rat heart model. Phosphamidon at a concentration range of 10(-6)-10(-3) M had a positive inotropic effect. Obidoxime at a concentration range of 10(-6)-10(-3) M had no significant effect on heart rate, but did have a statistically significant positive inotropic effect on end-systolic pressure, cardiac output, mean left ventricular pressure, and maximal time derivative of left ventricular pressure (dP/dtmax) (P less than 0.01). Perfusion with 10(-3) M obidoxime caused a 19% increase in left ventricular stroke work and a 31% increase in total pressure-volume area. Perfusion with phosphamidon and obidoxime at concentrations ranging from 10(-6) to 10(-3) M resulted in a more intense inotropic response than the separate drug effects. At the highest combined concentrations tested, cardiac output increased by 60%, left ventricular stroke work increased by 100%, and left ventricular total pressure volume area increased by 111% of their control values (P less than 0.001). We conclude that obidoxime augments the positive inotropic effect of phosphamidon on the isolated working rat heart.

Effect of phosphamidon and obidoxime on the QT-RR relationship of isolated rat heart

We studied the effects of phosphamidon (an organophosphate compound), obidoxime (a cholinesterase reactivator), and their combination, phosphamidon/obidoxime (PD/OB) on cardiac cycle length (RR), QT interval, and on QT-RR relationship of isolated rat heart. Cardiac cycle length did not change significantly following perfusion with phosphamidon or obidoxime alone; however, following perfusion with PD/OB, RR significantly increased at high concentrations (10(-3) M) of both drugs. The QT interval lengthened by 5% following perfusion with phosphamidon, did not change following perfusion with obidoxime, and increased by 10% following perfusion with PD/OB. The QT-RR relationship without drugs was positive and linear. Following perfusion with phosphamidon alone, the slope of the relationship decreased significantly, while perfusion with obidoxime alone did not change the QT-RR relationship. Perfusion with PD/OB at low concentrations decreased the slope of the relationship; however, at the highest concentration (10(-3) M) the QT-RR relationship was inverted and became negative. Ventricular arrhythmias as premature ventricular beats, or bigeminies, were noted with increasing frequency following perfusion with increasing doses of phosphamidon. Perfusion with obidoxime did not cause arrhythmias, whereas perfusion with PD/OB caused premature ventricular beats, bigeminies, and ventricular tachycardias at high doses. We suggest that obidoxime modulates the direct effects of phosphamidon on the cardiac repolarization process. PD/OB at high concentrations invert the normal depolarization-repolarization coupling and may therefore potentiate arrhythmias.