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2-adrenoceptors and
cAMP
Department of Physiology and Biochemistry, School of Medicine, University of São Paulo, Ribeirão Preto, 14049 - 900 São Paulo, Brazil
Overall proteolysis and the activity of skeletal muscle
proteolytic systems were investigated in rats 1, 2, or 4 days after adrenodemedullation. Adrenodemedullation reduced plasma
epinephrine by 95% and norepinephrine by 35% but did not affect
muscle norepinephrine content. In soleus and extensor digitorum longus
(EDL) muscles, rates of overall proteolysis increased by 15-20%
by 2 days after surgery but returned to normal levels after 4 days. The
rise in rates of protein degradation was accompanied by an increased
activity of Ca2+-dependent proteolysis in both muscles,
with no significant change in the activity of lysosomal and
ATP-dependent proteolytic systems. In vitro rates of
Ca2+-dependent proteolysis in soleus and EDL from normal
rats decreased by ~35% in the presence of either 10
5 M
clenbuterol, a 
2-adrenergic agonist, or epinephrine or
norepinephrine. In the presence of dibutyryl cAMP, proteolysis was
reduced by 62% in soleus and 34% in EDL. The data suggest that
catecholamines secreted by the adrenal medulla exert an inhibitory
control of Ca2+-dependent proteolysis in rat skeletal
muscle, mediated by 2-adrenoceptors, with the
participation of a cAMP-dependent pathway.
adrenodemedullation; epinephrine; clenbuterol; dibutyryl cyclic adenosine monophosphate; proteolytic systems
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