Direct effects of glucose administration on heart rate, myocardial contraction, and duration of cardiac cycle in frog's heart

Abstract

Background: Recent and emerging evidences show that glucose ingestion causes prolonged Q-T interval and can trigger arrhythmia. Objective: The objective of this study is to examine the effects of administration of glucose solutions on the heart rate, strength of myocardial contraction, and duration of the cardiac cycle in the frog's heart. Methods: Five pithed frogs with a mean weight of 119 g obtained from the research laboratory, Department of Human Physiology, Bayero University Kano, Nigeria, were dissected and their hearts were exposed; 2–3 drops of frog Ringer's solution were added regularly to keep the heart moist. A kymograph was used to record the frog's myocardial activity. This was also recorded after subsequent addition of 2 ml of 5%, 10%, and 50% dextrose solutions to the heart. Heart rate (b/min), strength of myocardial contraction (mm), and the duration of the cardiac cycle (seconds) were calculated. Data were analyzed using SPSS version 20.0 and the calculated parameters for each glucose solution were compared with that of frog's Ringer's solution using paired t-test. P < 0.05 is significant. Results: The result showed a significant decrease in the heart rate (b/min) from that obtained with Ringer's solution (54.40) after addition of 5%, 10%, and 50% dextrose solutions with mean heart rates of 50.40, 47.60, and 41.00, respectively. The height of myocardial contraction (mm) was found to be significantly decreased after addition of 50% dextrose solution only, with the mean heights for frog's Ringer's, 5%, 10%, and 50% dextrose solutions been 8.65, 8.90, 8.40, and 5.35, respectively. The duration of cardiac cycle in seconds was significantly increased after addition of 10% and 50% dextrose solutions, with the mean duration for the Ringer's, 5%, 10%, and 50% dextrose solutions been 1.11, 1.18, 1.26, and 1.47, respectively. Conclusion: Both 5%, 10%, and 50% dextrose solutions caused a significant decrease in frog's heart rate. Fifty percent dextrose solution caused a significant decrease in the strength of frog's myocardial contraction, and addition of both 10% and 50% dextrose solutions significantly increased the duration of cardiac cycle in frogs.