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Journal of Applied Physiology, Vol 80, Issue 3 999-1005, Copyright © 1996 by American Physiological Society
ARTICLES |
M. Van Soeren, T. Mohr, M. Kjaer and T. E. Graham
Faculty of Nursing, Health Sciences Centre, University of Western Ontario, London, Canada. mvansoer@julian.uwo.ca
Caffeine ingestion has been demonstrated to increase circulating epinephrine (Epi) and norepinephrine (NE), elevate free fatty acids (FFAs), and alter heart rate, blood pressure (BP), and ventilation in humans. Whether these physiological responses are a result of caffeine acting through direct stimulation of specific tissues via adenosine receptors or secondary to Epi increases is not known. In the present experiment, six tetraplegics (level of spinal cord lesions C4-C6) were tested at rest for 3 h to investigate the effects of 6 mg/kg caffeine in capsule form on subjects with impaired Epi responses. Ventilatory, cardiovascular, metabolic, and hormonal data were collected every 15-20 min after caffeine ingestion. There were no significant (P > 0.05) increases in plasma Epi after caffeine ingestion [0.19 +/- 0.04 (SE) nM (preingestion); 0.20 +/- 0.04 nM (80 min postingestion)] or in plasma NE [0.53 +/- 0.16 nM (preingestion); 0.49 +/- 0.09 nM (80 min postingestion; P > 0.05)]. However, significant increases were found in serum FFAs [0.53 +/- 0.08 nM (preingestion); 1.03 +/- 0.20 mM (40 min postingestion; P < 0.05] and in glycerol. These concentrations remained elevated throughout the experiment. BP increased in the first hour postingestion. These data demonstrate that caffeine in physiological doses directly stimulates specific tissues, i.e., adipose and peripheral vascular tissue, and these effects are not secondary to increases in Epi after caffeine ingestion.
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 J. A Greenberg, C. N Boozer, and A. Geliebter Coffee, diabetes, and weight control. Am. J. Clinical Nutrition, October 1, 2006; 84(4): 682 - 693. [Abstract] [Full Text] [PDF]
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K. J. Conway, R. Orr, and S. R. Stannard Effect of a divided caffeine dose on endurance cycling performance, postexercise urinary caffeine concentration, and plasma paraxanthine J Appl Physiol, April 1, 2003; 94(4): 1557 - 1562. [Abstract] [Full Text] [PDF]
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T. E Graham, J. W Helge, D. A MacLean, B. Kiens, and E. A Richter Caffeine ingestion does not alter carbohydrate or fat metabolism in human skeletal muscle during exercise J. Physiol., December 15, 2000; 529(3): 837 - 847. [Abstract] [Full Text] [PDF]
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T. J. Hawke, D. G. Allen, and M. I. Lindinger Paraxanthine, a caffeine metabolite, dose dependently increases [Ca2+]i in skeletal muscle J Appl Physiol, December 1, 2000; 89(6): 2312 - 2317. [Abstract] [Full Text] [PDF]
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F. Greer, D. Friars, and T. E. Graham Comparison of caffeine and theophylline ingestion: exercise metabolism and endurance J Appl Physiol, November 1, 2000; 89(5): 1837 - 1844. [Abstract] [Full Text] [PDF]
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M. H. Van Soeren and T. E. Graham Effect of caffeine on metabolism, exercise endurance, and catecholamine responses after withdrawal J Appl Physiol, October 1, 1998; 85(4): 1493 - 1501. [Abstract] [Full Text] [PDF]
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T. E. Graham, E. Hibbert, and P. Sathasivam Metabolic and exercise endurance effects of coffee and caffeine ingestion J Appl Physiol, September 1, 1998; 85(3): 883 - 889. [Abstract] [Full Text] [PDF]
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T. Mohr, M. Van Soeren, T. E. Graham, and M. Kjar Caffeine ingestion and metabolic responses of tetraplegic humans during electrical cycling J Appl Physiol, September 1, 1998; 85(3): 979 - 985. [Abstract] [Full Text] [PDF]
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E. M. R. Kovacs, J. H. C. H. Stegen, and F. Brouns Effect of caffeinated drinks on substrate metabolism, caffeine excretion, and performance J Appl Physiol, August 1, 1998; 85(2): 709 - 715. [Abstract] [Full Text] [PDF]
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