The uremic environment and muscle dysfunction in man and rat.
BACKGROUND
Patients reaching end-stage renal disease experience debilitating fatigue, with progression of this disease, rendering patients dysfunctional in their everyday lives.


METHODS
In vivo measurements of muscle function, assessed using surface electromyography (EMG), were made on 25 patients prior to and after a session of hemodialysis (HD) treatment, along side in vitro measurements of muscle function in isolated rat muscles incubated in normal or uremic conditions approximating to those found in uremic rats (rat uremic: RU) or uremic humans (human uremic: HU).


RESULTS
HD significantly affected plasma values, e.g. reducing urea (69%), creatinine (62%), potassium (23%) and phosphate (48%) concentrations in patients (all p < 0.01). Treatment also improved the EMG frequency of 2nd dorsal interosseous (fast-twitch) (p < 0.01), although no change was noted for vastus lateralis (slow-twitch). In isolated rat muscles, a uremic environment had no significant effect on slow-twitch soleus during field stimulation, however, in fast-twitch extensor digitorum longus, a significant 23% (RU) and 22% (HU) faster rate of decline in force was measured, compared to controls (p < 0.001 and p < 0.01, respectively).


CONCLUSIONS
It is concluded that (1) muscle weakness and its electrophysiological correlates may be rapidly induced by uremic solutes and rapidly reversed when the solutes are removed by dialysis, and (2) fast-twitch muscles are more readily affected by uremic conditions than slow-twitch muscles.
Harrison
A P
AP
Institute of Anatomy and Physiology, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark. adh@kvl.dk
Nielsen
A H
AH
Eidemak
I
I
Molsted
S
S
Bartels
E M
EM
D000328:Adult; D000368:Aged; D000818:Animals; D004576:Electromyography / Q000379:methods; D004777:Environment; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007676:Kidney Failure, Chronic / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018908:Muscle Weakness / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D014511:Uremia / Q000503:physiopathology*