Vasomodulation of skeletal muscle BOLD signal.
OBJECTIVE
To evaluate whether the BOLD signal from skeletal muscle can be modulated by exercise and ingestion of vasoactive substances.


METHODS
The right calf muscles of healthy adult volunteers were imaged using a GE 1.5-Tesla scanner and a gradient-echo sequence with spiral readout. Time-varying changes in the BOLD signal were induced through cyclic phases of normoxia (90 seconds of 20.8% O2) and hyperoxia (45 seconds of 100% O2 at 22 L/minute). Superimposed on this paradigm were pre- and post-exercise regimes, with and without ingestion of caffeine (100 mg) or antihistamine (4 mg chlorpheniramine). The numbers of voxels within slow-twitch (soleus) and fast-twitch (gastrocnemius) muscles that significantly responded to the paradigms were scored and compared using the AFNI software (NIMH).


RESULTS
Cycling-inspired O2 produced a corresponding BOLD modulation that increased in magnitude with exercise. Chlorpheniramine significantly (P<0.01) prevented the overall increase in exercise-induced soleus muscle BOLD signal, while caffeine accentuated the increase (P<0.05) in the gastrocnemius relative to control (no vasomodulator) conditions.


CONCLUSIONS
BOLD signal changes with exercise can be modulated by standard doses of chlorpheniramine (antihistamine) and caffeine. We suggest that chlorpheniramine may act detrimentally on slow-twitch muscle contractility, while caffeine appears to improve fast-twitch muscle function.
Bulte
Daniel P
DP
Functional Magnetic Resonance Imaging of the Brain (FMRIB) Centre, John Radcliffe Hospital, Headington, Oxfordshire, and Clinical Neurology, University of Oxford, United Kingdom.
Alfonsi
Jeff
J
Bells
Sonya
S
Noseworthy
Michael D
MD
D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D002110:Caffeine / Q000008:administration & dosage; D002744:Chlorpheniramine / Q000008:administration & dosage; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007866:Leg / Q000098:blood supply*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism; D012039:Regional Blood Flow / Q000502:physiology
D002110:Caffeine; D002744:Chlorpheniramine; D010100:Oxygen