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High-caffeine beverage increases cardiac sympathetic activity in Balb/c mice
Victor Chu, Jose M. Otero, Orlando Lopez, Ivo Amende, and Thomas G. Hampton; Mouse Specifics, Inc., Boston, MA. USA.
Web Published: August 1, 2001
Abstract
Caffeine content of soft drink beverages varies. Many individuals favor the stimuli provided by high-caffeine drinks. Potential health risks of super-caffeinated beverages have recently been discussed.1 To test whether caffeine affects heart rate and rhythm in mice, we non-invasively recorded electrocardiograms (ECGs) in 15 adult male Balb/c conscious mice provided with a soft drink containing 71.5 mg caffeine/12 oz. of beverage. We found that heart rate increased 6% (P<0.05) following caffeine ingestion compared to baseline. Time-domain heart rate variability indices significantly decreased following caffeine ingestion.
Methods
Figure 1.Baseline
Figure 2.Caffeine
Six-week old Balb/c mice were obtained from The Jackson Laboratory. The AnonyMOUSETM ECG screening system was used to record ECGs.2 Neither anesthetic nor surgery was required. Baseline recordings were performed following ad libitum access to water. Water bottles were then replaced with bottles containing a soft drink with 71.5 mg caffeine per 12 oz. The beverage was provided "flat" in the absence of carbonated gas. ECG recordings were repeated 24 hours later. Data were acquired at 2000 samples/s for at least 2 seconds to provide continuous recordings of 20 to 30 beats. e-MOUSETM was used to interpret the signals.2 Time domain indices of heart rate (HR) variability (var), e.g., HR var and coefficient of variance (CV%), were calculated as described by Gehrmann.3
Results
Each mouse consumed the approximate equivalent of 100 mg/kg caffeine over 24 hours. Heart rate significantly increased and HR var significantly decreased following caffeine ingestion. Table 1: Effects of Caffeine
Baseline (n=15)
Caffeine (n=15)
HR (bpm)
681 ± 11
725 ± 7*
PR (ms)
26.8 ± 0.5
26.3 ± 0.6*
HR var (bpm)
15 ± 2
8 ± 1*
CV (%)
5.3 ± 2.8
1.1 ± 0.2*
*P < 0.05 via Student's 2-tail paired
t-test.
Discussion
We found that in young adult male Balb/c mice, ingestion of a high-caffeine beverage over 24 hours resulted in a subtle but significant increase (6%) in heart rate and a significant decrease in HR variability. We did not detect any significant cardiac arrhythmias. The reported cardiovascular effects of caffeinated beverages vary.4,5 Although caffeine is commonly thought to cause tachycardia in humans6 , others have not found significant changes in heart rate.7 Caffeine is known to affect the central nervous system8, and our observations may be attributable to an increase in sympathetic tone in caffeine-treated Balb/c mice.
References
Winter, G. 2001. The New York Times May 1.
Chu, V. et al. 2001. BMC Physiology 1:6.
Gehrmann, J. et al. 2000. Am. J. Physiol. Heart Circ. Physiol. 279:H733-H740.
Chelsky, L.B. et al. 1990. JAMA 264:2236-2240.
van Dusseldorp, M. et al. 1989. Hypertension 14:563-569.
Myers, M.G. 1991. Ann. Intern. Med. 114:147-150.
Donnerstein, R.L. et al. 1998. Am Heart J 136:643-646.
Quinlan, P.T. et al. 2000. Pharmacol. Biochem. Behav. 66:19-28.
