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| ORIGINAL ARTICLE |
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| Year : 2018 | Volume
: 4
| Issue : 1 | Page : 29-32 |
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Direct effects of glucose administration on heart rate, myocardial contraction, and duration of cardiac cycle in frog's heart
BI Waziri, A Shahzad
Department of Human Physiology, Faculty of Basic Medical Sciences, College of Health Sciences, Bayero University Kano, Kano, Nigeria
| Date of Web Publication | 4-May-2018 |
Correspondence Address:
Dr. B I Waziri
Department of Human Physiology, Faculty of Basic Medical Sciences, College of Health Sciences, Bayero University Kano, Kano
Nigeria
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jpcs.jpcs_9_18
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. Keywords: Cardiac cycle, dextrose solution, heart rate, myocardial contraction
How to cite this article:
Waziri B I, Shahzad A. Direct effects of glucose administration on heart rate, myocardial contraction, and duration of cardiac cycle in frog's heart. J Pract Cardiovasc Sci 2018;4:29-32 |
How to cite this URL:
Waziri B I, Shahzad A. Direct effects of glucose administration on heart rate, myocardial contraction, and duration of cardiac cycle in frog's heart. J Pract Cardiovasc Sci [serial online] 2018 [cited 2023 May 31];4:29-32. Available from: https://www.j-pcs.org/text.asp?2018/4/1/29/231940 |
| Introduction | |  |
Dextrose solutions have been used worldwide in the management of patients in our hospitals suffering from one form of disease or another. One of the most common conditions where dextrose is administered through parenteral route is in the management of severe hypoglycemia usually characterized by impaired level of consciousness and seizures occasionally,[1] thus preventing the patient from taking oral glucose.[2] The common practice involves intravenous (IV) administration of 50% dextrose for adults presenting with hypoglycemia and 10% to 25% for children with the same condition.[2] Recent evidences have also shown that, even in the adults, IV infusion of 100 ml of 10% dextrose solution is an alternative to 50 ml of 50% dextrose in the treatment of hypoglycemia and it reduces the risk of extravasation injury and other toxic effect of hypertonic dextrose.[3] Dextrose solutions were also reported to be used during resuscitation of patients with cardiac arrest in order to prevent or reverse hypoglycemia.[4]
Researches have shown that glucose ingestion or administration affects cardiac function.[5] More recently, it has been found that glucose ingestion causes cardiac repolarization disturbances and prolong QTc interval leading to increased risk of cardiac arrhythmia.[5],[6] It was also reported that administration of dextrose in a patient with cardiac arrest in the hospital is associated with increased mortality and neurologic impairment.[4] The alteration in cardiac function following glucose administration is partly due to autonomic and endocrine responses to elevated plasma glucose.[7] Data on the direct and immediate effects of glucose administration on the heart itself are scanty and need to be further investigated.
This study assessed the direct and immediate effects of dextrose administration on the heart rate, duration of cardiac cycle, and myocardial contractility in frog's heart.
| Methods | | |
The study was conducted in the research laboratory, Department of Human Physiology, Faculty of Basic Medical Sciences, College of Health Sciences, Bayero University Kano, Nigeria. Five pithed frogs with a mean weight of 119 g were obtained from the laboratory and placed on dissecting boards. For each frog, a small incision was made into the abdominal cavity using the sharp end of scissors and the abdominal wall was dissected carefully with dissecting kits. The sternum was lifted up and its sides were cut together with the pectoral girdle to expose the heart in its pericardial sac. The sac was then excised and removed carefully, thus exposing the heart completely. A heart clip attached to a thread was then inserted to the apex of the ventricles, and the frog was positioned on a frog board attached to a kymograph in such a way that the heart lied vertically and below the attachment of the clip. The thread was then connected to the recording pen on the kymograph. Two to three drops of frog's Ringer's solution (containing 3.6 g NaCl, 0.1 g KCl, 0.1 g CaCl2,0.9 g glucose, and 0.2 g MgCl2 in 500 ml of the solution) were added to the heart regularly at interval of 30 s after the exposure. Finally, the kymograph was then switched on to record the frog's myocardial activity in 1 min. The myocardial activity was first recorded 30 s after addition of 2 ml of Ringer's solution and then subsequently 30 s after addition of the same amount of 5%, 10%, and 50% dextrose solutions each. The heart rate (b/min) was calculated from the graph by counting the number of contractions in 1 min. The duration of cardiac cycle (seconds) was estimated by dividing 60 s with the heart rate (duration of cardiac cycle = 60/heart rate) and the strength of myocardial contraction was estimated by measuring the average height of the contractions (mm) using a meter rule.
Data were summarized and presented as means ± standard error of the mean and analyzed using SPSS version 20.0 (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.). Mean heart rate, duration of cardiac cycle, and strength of myocardial contraction for each dextrose solution were compared with that obtained from addition of frog Ringer's solution (control) using paired t-test. P < 0.05 was considered statistically significant.
| Results | | |
The result shows a significant decrease (P< 0.05) in the heart rate from that obtained with Ringer's solution (54. 40 ± 0.51) after addition of 5%, 10%, and 50% dextrose solutions with mean heart rates of 50.40 ± 0.93, 47.6 ± 0.68, and 41.00 ± 1.22, respectively [Figure 1], [Figure 2], [Figure 3]. The decrease is proportional to the concentration of glucose in the solution. | Figure 1: The frog's heart rate (b/min) obtained after addition of 2 ml of frog Ringer's, 5%, 10%, and 50% dextrose solutions. * = significant (P < 0.05).
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 | Figure 2: The duration of cardiac cycle (seconds) obtained addition of frog Ringer's, 5%, 10%, and 50% dextrose solutions. * = significant (P < 0.05).
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 | Figure 3: The strength of myocardial contraction (mm) following addition of frog Ringer's, 5%, 10%, and 50% dextrose solutions. * = significant (P < 0.05).
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The result shows a significant increase in the duration of cardiac cycle following the addition of 10% and 50% dextrose solutions compared with that obtained from the addition of Ringer's solution (control) with the mean durations for Ringer's, 5%, 10%, and 50% dextrose been 1.11 ± 0.01, 1.18 ± 0.02, 1.26 ± 0.01, and 1.47 ± 0.05, respectively. The increase in the duration of cardiac cycle following the addition of 5% dextrose was not statistically significant.
The result shows a significant decrease in the strength of myocardial contraction after addition of 50% dextrose solution only in comparison with the control with the mean strength of myocardial contraction for Ringer's, 5%, 10%, and 50% dextrose solutions been 8.65 ± 0.24, 8.90 ± 0.37, 8.40 ± 0.13, and 5.35 ± 0.71, respectively. There was a slight increase in the strength of myocardial contraction following the addition of 5% dextrose solution. However, it was not statistically significant.
| Discussions | | |
The heart rate reduced significantly following the addition of 5%, 10%, and 50% dextrose solutions and the reduction was proportional to the concentration of glucose in the solutions. This might be due direct effect of glucose on the intrinsic heart rate. It was reported that hyperglycemia and glucose intolerance as in metabolic syndrome reduce the rate of spontaneous firing of the sinoatrial (SA) nodal cells.[8] Our finding is in agreement with that of Schaan et al.,[9] who also found a decrease in heart rate in Streptozotocin-induced diabetes rats just 5–7 days after the induction. They suggested that the decrease in the heart rate was possibly due to effect of hyperglycemia on the intrinsic node function. Contrary to this, other researchers [7],[10] have reported increase in heart rate due to elevated plasma glucose level, but this might be due to autonomic and endocrine responses to hyperglycemia such as increased sympathetic activity, which in turn causes an increase in heart rate unlike in this present study where the immediate and direct effect of dextrose administration on the heart itself was assessed.
The duration of the cardiac cycle was significantly prolonged following administration of 10% and 50% dextrose solutions. No significant change was found after addition of 5% dextrose. This has indicated that high glucose concentration might interfere with impulse generation, its spread, and conduction in the heart. It has been reported that acute hyperglycemia in healthy subjects causes an increase in P-R interval [11] indicating slow atrioventricular conductivity and prolong QTc [11] indicating impaired depolarization or repolarization, all of which can result to increase in the duration of cardiac cycle. Recently, researchers found that glucose ingestion and hyperglycemia cause cardiac repolarization disturbances, characterized by prolong QTc interval.[5],[6] It has been suggested that elevated level of glucose might suppress the function of Ikr ion channels responsible for potassium extrusion, therefore resulting to delay in cardiac repolarization [12] which in turn increases the cardiac cycle duration. Elevation in intracellular glucose was also found to modify the effects of dofetilide (a potent pro-arrhythmic agent) acting directly on Ikr channels resulting to decrease potassium efflux and prolong QTc.[5]
The strength of the myocardial contraction was found to be significantly reduced following the addition of 50% dextrose solution to the heart. No significant changes were observed with 5% and 10% dextrose solutions. This has indicated that hypertonic dextrose has a negative effect on the strength of myocardial contraction. This is possibly due to its toxic effect on tissues as it is known that hypertonic solution can cause vascular injury and tissue necrosis.[13] It was also reported that hyperglycemia has a negative effect on myocardial blood flow and perfusion [14] which can also result to decrease in the strength of myocardial contraction. Our findings are in support of a previous study [9] where they demonstrated that hyperglycemia results to myocardial dysfunction and decrease force of myocardial contraction.
| Conclusion | | |
Direct administration of 5%, 10%, and 50% dextrose solutions to the frog's heart caused a significant decrease in the heart rate, 10% and 50% dextrose significantly prolonged the duration of the cardiac cycle, and the strength of myocardial contractility was significantly reduced following administration of 50% dextrose solution.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
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