In vitro effect of branched chain amino acids on the ribosomal cycle in muscles of fasted rats.

1) The effect of a single i.p injection of branched chain amino acids on ribosomal profiles of psoas muscles was studied in rats after a 48--96 hour fast. Experimental and control animals received glucose and insulin 1--2 hours before killing. 2) The ratio of polysomes to subunits and monomers decreased progressively during the fast. 3) The administration of the three branched chain amino acids together or leucine alone significantly increased the proportion of polysomes. 4) This effect was not observed in rats fed ad libitum. 5) It is suggested that the branched chain amino acids and specifically leucine may be required for the full protein anabolic response of muscles to insulin during a prolonged fast.