Amino acid uptake in skeletal muscle of rats bearing the Yoshida AH-130 ascites hepatoma.

Rats bearing the Yoshida AH-130 ascites hepatoma show decreased activity of neutral amino acid transport in skeletal muscle measured in vivo as the tissue accumulation of the analogue alpha-amino [1-14C]isobutyrate (AIB). The decreased accumulation of AIB observed is not merely a consequence of the hypoinsulinaemia present in these animals (as a result of tumour burden) since in vitro experiments carried out using incubations of isolated soleus muscles also showed a decreased uptake of neutral amino acids. In these preparations the addition of insulin results in similar increases in uptake both in the pair-fed controls and the tumour-bearing animals, thus suggesting similar insulin sensitivities. The decrease in amino acid uptake in soleus muscle is associated with a decrease in the activity of system A, while systems L and ASC show no particular changes as a result of the tumour growth. The kinetic characterisation of system A in the Yoshida-bearing rats shows a decrease in Vmax together with a decrease in KM in relation with the pair-fed animals.