Phentolamine effect on the spontaneous electrical activity of active loci in a myofascial trigger spot of rabbit skeletal muscle.
OBJECTIVE
To investigate the effect of phentolamine, a sympathetic blocking agent, on the spontaneous electrical activity (SEA) recorded from a locus of a myofascial trigger spot (MTrS), equivalent to a human trigger point, in rabbit skeletal muscle.


METHODS
Randomized control trial.


METHODS
A university medical laboratory.


METHODS
Nine adult New Zealand rabbits.


METHODS
In the experimental group phentolamine mesylate (1mg/kg) was injected into the external iliac artery, followed by flushing with normal saline. The control group was treated with normal saline instead of phentolamine using the same procedure.


METHODS
SEA was recorded from multiple active loci of MTrSs in the biceps femoris muscle: initially SEA in the same locus was recorded before and immediately after phentolamine (or normal saline) injection; then SEA was recorded from 25 different active loci. The mean of the average integrated signal (AIS) of SEA was analyzed, comparing the effects of phentolamine and normal saline on SEA.


RESULTS
In the same active locus, the AIS of SEA showed statistically a linear decay with time after phentolamine injection, with a correlation coefficient of .56 at p < .05. However, no statistical relationship could be derived for the control group data with time by using regression analysis, probably because of large variations among the rabbits and movement artifacts during the experiment. In 25 different loci in the phentolamine group, the mean of the AIS of SEA (7.92 microV) was significantly lower than that of the control group (9.89 microV) at p < .05.


CONCLUSIONS
The results support the hypothesis that the autonomic nervous system is involved in the pathogenesis of myofascial trigger points. The application of the AIS as an evaluation index seems to be feasible in the quantitative measurement of SEA.
Chen
J T
JT
Department of Physical Medicine and Rehabilitation, National Cheng-Kung University Hospital, Tainan, Taiwan.
Chen
S M
SM
Kuan
T S
TS
Chung
K C
KC
Hong
C Z
CZ
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000328:Adult; D000818:Animals; D004576:Electromyography / Q000187:drug effects; D006801:Humans; D007269:Injections, Intra-Arterial; D008564:Membrane Potentials / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000503:physiopathology; D009209:Myofascial Pain Syndromes / Q000503:physiopathology*; D010646:Phentolamine / Q000494:pharmacology*; D011817:Rabbits; D012815:Signal Processing, Computer-Assisted
D000317:Adrenergic alpha-Antagonists; D010646:Phentolamine