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Medical Research Society
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150
MECHANISMS OF INHIBITION OF INTRACELLULAR ENZYME
EFFLUX FROM DAMAGED SKELETAL MUSCLE BY '" -TOCOPHEROL AND
RELATED COMPOUNDS.
J Phoenix, R H T Edwards, and M J Jackson
Department of Medicine, The University of Liverpcol
Vitamin E appears to be impcrtant in the maintenance
of normal muscle structure with dietary depletion resulting in increased intracellular enzyme efflux following
contractile activity (Jackson et al. Ciba Foundation
Sympcsia 101:224,1983) and enzyme release from damaged
normal muscles in vitro inhibited by ~ -tocopherol (Poole
et al. Proc. Nutr. Soc. 47:34A,1987). This latter effect
was mimicked by II( -tocopherol acetate, phytol and isophytol suggesting a non-antioxidant role in this system
and we have therefore examined other potential protective
mechanisms.
Treatment of isolated rat soleus muscles with calcium
ionophore, A23187 (20~) in the presence or absence of
0( -tocopherol
(230~) induced a significantly lower
release of creatine kinase from the tocopherol treated
muscles (27mU/30mins/muscle ± 11 at 90mins. post ionophore treatment cf. controls 159 ± 11), although the
total calcium content of both groups of muscles was
significantly elevated compared to untreated controls.
The ionophore stimulated release of prostaglandin E was
2
unaffected by tocopherol (7.90±1.95 pg/mg/30mins cf.
controls: 10.32!3.13) demonstrating that tocopherol was
not acting to inhibit phospholipase enzymes.
Preliminary studies of the effects of tocopherol and
related compounds on lipoxygenase activity have revealed
that phytol and isophytol have a similar inhibitory
effect to '" -tocopherol (mean inhibition: '" -tocopherol
(230~) 46.7%; phytol (230~) 57.8%; isophytol (230~)
45.6%). These results suggest that inhibition of intracellular enzyme efflux from skeletal muscle by vitamin E
is not related solely to an antioxidant
function but is
dependent upon the phytyl side chain and may be linked to
an inhibition of lipoxygenase activity
Supported by the Muscular Dystrophy Group of Great
Britian and Northern Ireland and F.Hoffmann LaRoche and
Co. ,Ltd.
EFFECT OF LOW FREQUENCY FATIGUE ON HUSCLE
ENOORANCE CAPACITY
151
RG Cooper, MJ Stokes, & RHT Edwards.
This confirmation that LFF persists during
activity and reduces low but not high frequency
fatigue resistance suggests that impaired endurance
during voluntary activity primarily results from
peripheral changes at low frequency.
Supported by the Muscular Dystrophy Group of Great
Britain & Northern Ireland, and ICI Pharmaceuticals.
152 GLUTAnlIONE PEROnDASE ACTIVITY AND SELEKIUM
mERAPT Df MUSCULAR DYSTROPHIES.
Coakley JH, Stokes MJ, Oster 0*, Edwards RHT and
Jackson MJ.
Muscle Research Centre, Department of Medicine,
University of Liverpool, L69 3BX *Clinical
Chemistry Laboratory, University Of Mainz, BRD
Muscular dystrophy (MD) may be associated with a
low plasma selenium (Se) and increased Se turnover
(Acta Pharmacol et Toxicol (1977) 41, 121: Klin
Paediat (1982) 194, 301). Therapeutic trials of Se
in myotonic MD ( Acta Med Scand (1982) 211, 237) and
Duchenne dystrophy (DMD) (J Child Neurol (1986) 1,
211) have suggested a beneficial effect. Se is an
essential part of the enzyme glutathione peroxidase
(GSHPx) which protects membrane lipids from free
radical damage. Evidence of increased free radical
activity in dystrophic muscle (Med Biol (1984) 62,
143) prompted the present study which attempted to
increase musc 1 e GS HP x act i v i t Y wit h S e
supplementation.
Three groups were studied: adult MDs (Group A for
2 months n=19) boys with DMD (Group B for 6 months
n=10) and healthy adult controls (Group B for 2
months n=8). Mean values for GSHPx acti vi ty (U / g
soluble protein) were:
Group A
Group B
Group C
Before
15.7+5.7
24.6+13.1
20.0.!7.4
After
20.1+5.5
19.3+8.3
18.0=.2.3
The di fferences between treatment groups were not
significant before and after Se. We conclude that
Se supplementation did not increase muscle GSHPx
activity within the time period of the present
study.
Supported by the Muscular Dystrophy Group of Great
Britain and Northern Ireland.
Muscle Research Centre, Department of Medicine,
University of Liverpool, PO Box147, L69 3BX.
Low frequency fatigue (LFF) after exercise
(Edwards et al., J Physiol,1977 272: 769) reduces
endurance capacity during subsequent voluntary
activity (Sargeant & Dolan, Eur J Appl Physiol, 1987
56:704) and increases perception of effort (Gandevia
& McCloskey, Brain, 1982 105:151). The present
study examines the effects of LFF on fatigue
resistance during stimulated contractions in 6
healthy adults. Supramaximal stimulation of the
ulnar nerve, in a set frequency pattern (1, 10, 20,
50 100 & 1 Hz for 2 sees each), produced
contractions of adductor pollicis (Cooper et a1., J
Physiol, 1988 397:585). Simultaneous recorQIngs of
isometric force and surface electromyography
produced the programmed stimulation electromyogram
(PSEM). Fatiguing activity consisted of 20 PSEMs
with a 5 sec rest between each (Run i ), After 15
mins recovery) when LFF was evident, the protocol
was repeated (Run 2).
Force at low frequencies was potentiated in Run
1, reduced in recovery (LFF) and declined further in
Run 2 despite unchanged excitation.
This
increased fatiguability at low frequency did not
affect fatiguability at high frequency where force
and excitation declined similarly during both runs
(evg, Table).
FORCE
Frequency
Run 1
Run 2
(Hz)
110+49
60+19
10
100
66~9
68
EXCITATION
Run 1
Run 2
104+15
101+20
4~15
4~21
Table Changes in force and excitation, as a % of
values at the start of each run (mean=. 1 SD).
NO ISCHAEHIC RECOVERY CF mE EVOKED COMPOUND MUSCLE
ACTION POTENTIAL Df "IcARDLE'S DISEASE
153
H GIBSON AND RHT EDWARDS
t1uscle Research Centre, Department of l1edicine,
University of Liverpool, L69 3BX
In McArdle's disease (myophosphorylase
deficiency), the recovery of the evoked surface compound
muscle action potential (CMAP) amplitude of the adductor
pollicis (AP) following stimulated activity does not
occur anaerobically (Edwards et al., In: Disorders of
the Motor unit, Ed, Schotland D., Wiley Med, 1982). The
present study examines further the anaerobic recovery of
CMAP characteristics following anaerobic activity.
Supramaximal stimulation of the AP was delivered via the
ulnar nerve at the wrist at 20Hz for 1050 impulses in
two patients with McArdle's disease. Ischaemic recovery
of CMAP amplitude and conduction velocity (measured from
the start of rise of the first negative phase to peak)
were studied at intervals for up to one minute and
compared to those in three normal subjects following the
same stimulation procedure and also after 2400 impulses.
In patients, CMAP amplitude was markedly reduced
to 29.4% & 53.0% and did not recover until circulatior
was restored. Conduction velocity did not change. Ir
normal subjects, CM.AP amplitude declined to a similar
extent only after the greater activity but recoveree