Acute effects of caffeine ingestion at rest in humans with impaired
epinephrine responses.
Soeren, M. Van, T. Mohr, M. Kjaer, and T. E. Graham.
Faculty of Nursing, Health Sciences Centre, University of Western
Ontario, London, ONTARIO, Canada, N6A 5C1, Department of Medical
Physiology, Panum Institute, Copenhagen Muscle Research Centre and
Department H Bispedjerg Hospital, University of Copenhagen,
Copenhagen, DENMARK, Human Biology, University of Guelph, Guelph,
ONTARIO, Canada, N2G 2W1
APStracts 2:0470A, 1995.
Caffeine ingestion has been demonstrated to increase circulating
epinephrine (E) and norepinephrine (NE), elevate free fatty acids
(FFA) 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 E increases is not known. In the
present experiment, six tetraplegics (level of spinal cord lesions C4
- C6) were tested at rest for 3 hours to investigate the effects of 6
mg/kg caffeine in capsule form on subjects with impaired epinephrine
responses. Ventilatory, cardiovascular, metabolic and hormonal data
were collected every 15 - 20 min following caffeine ingestion. There
were no significant (p>0.05) increases in plasma E following
caffeine ingestion (pre-ingestion, 0.19 +/- 0.04; 80 min post
-ingestion, 0.20+/- 0.04 nM) (mean +/- SE) nor in plasma NE (pre
-ingestion, 0.53+/- 0.16; 80 min post-ingestion, 0.49+/- 0.09 nM)
(p>0.05). However, significant increases were found in serum FFA
(pre-ingestion, 0.53 +/- 0.08; 40 min post-ingestion, 1.03 +/- 0.20
mM) (p<0.05) and in glycerol. These concentrations remained
elevated throughout the experiment. BP increased in the first hour
post-ingestion. 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 E following caffeine ingestion.
Received 21 June 1995; accepted in final form 18 October 1995.
APS Manuscript Number A662-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95