QT and QTc prolongation and decreased heart rate after IV administration of levamisole hydrochloride in conscious rabbits

Intravenous doses of 2.5 mg/kg and 5.0 mg/kg of levamisole on RR, QT, QTc (corrected QT), and heart rate in conscious rabbits were evaluated. The study was performed on 14 New Zealand rabbits, 1 year old, weighing between 2.5-3 kg. The animals were assigned to 2 equal groups. Rabbits of groups I and II received via the auricular vein 2.5 mg/kg and 5 mg/kg of levamisole HCl, respectively. Alligator clips were attached to four limbs. ECG records were taken by direct writing electrocardiograph before the study and after 2, 4, 6, 8, 10, 15, and 20 min of the experiment. The QT interval was manually calculated from the beginning of Q wave to the end of T wave. The same leads (II and aVR) were selected for all QT interval measurement. The animals were not given any sedatives or anaesthetics before and during ECG recording. In group I, two rabbits had the second degree atrial block at the 2(nd) and 4(th) min after the injection, which disappeared later. Heart rates were 216-230 beats/min at min 0 and dropped to 193-210 beats/min at the 2(nd) min after the injection in both groups, and remained low throughout the study. Heart rates of both groups taken at 2, 4, 6, 8, 10, 15, and 20 min after the injection were significantly lower than the values taken at 0 min except for the values of the 15(th) min in group II. QT and QTc prolongation was noticed in both groups when compared to 0 min values. Although we have no solid data to explain the mechanism involved in bradycardia and atrial block provoked by levamisole, its use resulted in bradycardia, second-degree atrial block, and acute prolongation of QT and QTc in conscious rabbits

QT interval prolongation and decreased heart rates after intravenous bolus oxytocin injection in male and female conscious rabbits

The aim of this study was to evaluate changes in heart rate (HR), QT and RR intervals and corrected QT (QTc) values in conscious male and female New Zealand rabbits which intravenously received oxytocin (OXT) at different dosages. Animals were divided into 6 equal groups: group I (n = 6 male, received 0.75 U OXT per animal); group 11 (n = 6 male, received 1.5 U OXT per animal); group III (n = 6 male, received 3 U OXT per animal); group TV (n = 6 female, received 0.75 U OXT per animal); group V (n = 6 female, received 1.5 U OXT per animal); group VI (n = 6 female, received 3 U OXT per animal). ECG recording were taken from all animals before injection and then at 2, 4, 6, 8, 10, 15 and 20 min of OXT administration. QT and RR intervals obtained at 2 min of OXT administration were significantly prolonged in all groups (p < 0.05) with one exception that is the 1.5 U OXT injected female group where only QT interval did not change. The prolongation of QT and RR intervals persisted for 20 min in 1.5 U OXT injected male group while only QT interval prolongation was obvious for 20 min in 3 U OXT injected female group as for the other groups the prolonged interval were observed for 8-10 min and then returned to baseline values. Generally, a significant prolongation of QTc was noticed in both male and female rabbits at the 2 and 4 min in all groups and bradycardia was noticed at 2 min of OXT administration in all groups. Heart beats returned to normal values in all groups after 8 min of OXT administration. The change of HR, RR, QT and QTc was gender- but not dose-dependent (p < 0.001). The male rabbits were more sensitive to OXT effect then female rabbits. In conclusion, OXT used in therapeutic dosages decreased heart rate and prolonged QT and QTc intervals. Although cardiovascular effect of OXT are of short duration, its use in patient with risk factors for malignant arrhythmias requires more attention

Effects of different nonsteroid antiinflammatory drugs on free triiodothyronin (fT(3)), free thyroxin (fT(4)) and thyroid stimulating hormone concentration in rabbits

This study was aimed to investigate the effects of commonly prescribed NSAIDs, flunixin meglumine, carprofen and meloxicam, on the concentrations of free triiodothyronin (fT(3)), free thyroxin (fT(4)) and thyroid stimulating hormone in healthy rabbits. For this purpose, 32 New Zealand rabbits of similar age and weight and different sex were divided into four equal groups of eight. Rabbits in control group (n=8) received serum physiologic, animals in group FLU (n=8) were given flunixin meglumine at dose of 1.1 mg/kg, group CAR (n=8) received 2.2 mg/kg carprofen and group MEL (n=8) was given 0.2 mg/kg meloxicam intramuscularly (IM) for 5 days. Blood samples were collected 4 hours after each injection from vena auricularis into plain vials to determine hormone concentrations. Following separation of serum by centrifugation at 3000 rpm for 10 minutes, commercially available ELISA kits for free T(3), freeT(3) and TSH were used for determination. Results shown that fT(3), and fT(4) concentrations increased throughout the study period of 5 days within 3 treatment groups (p<0.001) and these increases were also significant when compared to control group (p<0.05, p<0.01 and p<0.001) while TSH concentrations decreased in treatment groups (p<0.001) during the study period and it was also lower than the control group (p<0.001). In conclusion, use of NSAIDs can alter thyroid hormone concentrations and thus these alterations should be considered in diagnosis and therapy in order to avoid misleading