ABSTRACT
This work was designed to investigate the reactivity of isolated hearts and aortic strips from normal rabbits and experimentally induced diabetic ones whether nontreated or treated with insulin or glybenclamide.In addition, the effect of cimetidine [H2 - blocker] and pheneramine maleate [HI - blocker] on the isolated rabbit hearts was studied in the 4 different groups.It was found that histamine induced a significant increase in the heart rate in a dose dependent manner in the control group with all doses used, and in the insulin and glybenclamide treated groups in the larger doses [50, 100 ug / ml]. Histamine also induced a significant increase in the amplitude of ventricular contraction in a dose dependant manner in the control and the insulin treated groups in all doses used and in the glybenclamide treated group with doses of 50, 100 ug/ ml but with a great significance In the diabetic group, this increase in the heart rate and the amplitude of ventricular contraction was found to be insignificant, However, there was a great significant reduction in the percentage of change in both parameters when compared to the control group. Histamine induced arrhythmia at a dose of 100 ug in the control, the insulin treated and the glybenclamide treated groups.With respect to the cardiac reactivity to hisamine antagonists, it was found that H2 blockers had a significant reduction in the heart rate and in the amplitude of ventricular contraction in the 4 groups studied without any significant change between them. Concerning the vascular reactivity to different doses of histamine, it was found that histamine induced a dose dependant increase in the tension developed, the time to reach maximum contraction and the time of maintained tone responses of aortic strips trom the 4 groups studied, No significant change was detected between the 4 different groups. However, it was clear that diabetes affected the vascular reactivity of rabbit aortic strips through significant prolongation in the time to reach relaxation in all doses used. In addition, insulin treatment decreased the time to reach relaxation response of the diabetic aortic strips, while glybenclamide treatment decreased it in one dose only, Therefore, it could be concluded that histamine has a positive inotropic and chronotropic effects while H2 blocking drugs have a cardiodepressant properties and that histamine in large doses causes arrhythmia and cardiac dysfunction. The.diabetic rabbit hearts have subnormal responsiveness to histamine stimulation and resist the occurrence of arrhythmia induced by histamine. This diabetic response can be completely normalized by insulin treatment, while glybenclamide treatment improves only the chronotropic response