Anormalidades neuromuscular no desuso, senilidade e caquexia

Neuromuscular abnormalities in disuse, cachexia and ageing

Resumos

É feita revisão de literatura sobre as principais alterações do sistema neuromuscular no desuso, senilidade e caquexia no ser humano e em modelos animais. A diminuição do diâmetro das fibras musculares após período de inatividade/imobilidade (desuso) deve-se à perda de miofibrilas periféricas não ocorrendo formação de core-targetóides ou diminuição da atividade da miofosforilase, próprias da desnervação; mantêm-se a liberação espontânea de acetilcolina e fatores tróficos na junção mio-neural; em geral são afetadas preferencialmente fibras II, que podem assumir forma angular. Existe um processo contínuo intrínseco de envelhecimento de nervos e músculos, com desnervação e reinervação lenta e progressiva; o número de unidades motoras se reduz após 60 anos, sem ocorrência de atividade elétrica desnervatória; a quantidade de acetilcolina liberada nos neurônios terminais e a capacidade máxima de utilização de oxigênio estão diminuídas; a redução da capacidade oxidativa mitocondrial pode explicar o aumento de fibras I, mantendo-se o equilíbrio energético. Após poucas semanas de caquexia as fibras musculares podem ter o diâmetro reduzido em 30%, essa redução ocorre em ordem decrescente nos músculos dos membros inferiores, superiores e tronco; existe atrofia II preferencial com fibras angulares ocasionais, redução de RNA/síntese proteica, mantendo-se DNA normal.

caquexia; envelhecimento; imobilização; doenças neuromusculares


Cachexia, ageing and disuse and their effects on the human and animals neuromuscular system are reviewed. Disuse induces reduction of muscle fibers (mainly II) diameter with peripheral myofibrils lost; there is no core-targetoid or even reduction on myophosphorilase activity, both typical of denervation; the acetylcholine spontaneous release and trophic factors on myoneural junction are maintained; muscle fibers could change to angular shape. Ageing affects nerve and muscle by a continuous and progressive process of denervation and reinner-vation; the number of motor units diminishes in sixties without any denervation electric activity; there is also reduction on the amount of ACh release on terminal neurons and mitochondrial oxidative capacity leading to compensatory type I muscle fiber number increase. Cachexia also induces reduction on muscle fibers diameter first on legs and then on arms and trunk; there is type II atrophy with occasional angular fibers, RNA/proteic synthesis reduction and normal DNA.

cachexia; ageing; immobilization; neuromuscular diseases


João Aris Kouyoumdjian

Professor Assistente da Disciplina de Neurologia da Faculdade de Medicina de São José do Rio Preto

RESUMO

É feita revisão de literatura sobre as principais alterações do sistema neuromuscular no desuso, senilidade e caquexia no ser humano e em modelos animais. A diminuição do diâmetro das fibras musculares após período de inatividade/imobilidade (desuso) deve-se à perda de miofibrilas periféricas não ocorrendo formação de core-targetóides ou diminuição da atividade da miofosforilase, próprias da desnervação; mantêm-se a liberação espontânea de acetilcolina e fatores tróficos na junção mio-neural; em geral são afetadas preferencialmente fibras II, que podem assumir forma angular. Existe um processo contínuo intrínseco de envelhecimento de nervos e músculos, com desnervação e reinervação lenta e progressiva; o número de unidades motoras se reduz após 60 anos, sem ocorrência de atividade elétrica desnervatória; a quantidade de acetilcolina liberada nos neurônios terminais e a capacidade máxima de utilização de oxigênio estão diminuídas; a redução da capacidade oxidativa mitocondrial pode explicar o aumento de fibras I, mantendo-se o equilíbrio energético. Após poucas semanas de caquexia as fibras musculares podem ter o diâmetro reduzido em 30%, essa redução ocorre em ordem decrescente nos músculos dos membros inferiores, superiores e tronco; existe atrofia II preferencial com fibras angulares ocasionais, redução de RNA/síntese proteica, mantendo-se DNA normal.

Palavras-chave: caquexia, envelhecimento, imobilização, doenças neuromusculares.

SUMMARY

Cachexia, ageing and disuse and their effects on the human and animals neuromuscular system are reviewed. Disuse induces reduction of muscle fibers (mainly II) diameter with peripheral myofibrils lost; there is no core-targetoid or even reduction on myophosphorilase activity, both typical of denervation; the acetylcholine spontaneous release and trophic factors on myoneural junction are maintained; muscle fibers could change to angular shape. Ageing affects nerve and muscle by a continuous and progressive process of denervation and reinner-vation; the number of motor units diminishes in sixties without any denervation electric activity; there is also reduction on the amount of ACh release on terminal neurons and mitochondrial oxidative capacity leading to compensatory type I muscle fiber number increase. Cachexia also induces reduction on muscle fibers diameter first on legs and then on arms and trunk; there is type II atrophy with occasional angular fibers, RNA/proteic synthesis reduction and normal DNA.

Key words: cachexia, ageing, immobilization, neuromuscular diseases.

Full text available only in PDF format.

Texto completo disponível apenas em PDF.

Aceite: 3-março-1903.

Dr. João Aris Kouyoumdjian — Av. Bady Bassitt 3896 - 15026-000 Sao José do Rio Preto SP -Brasil.

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  • Anormalidades neuromuscular no desuso, senilidade e caquexia
    Neuromuscular abnormalities in disuse, cachexia and ageing

Datas de Publicação

  • Publicação nesta coleção
    19 Jan 2011
  • Data do Fascículo
    Set 1993
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