In a parallel-group design , @ healthy older men ( aged @ @ y ) received a primed continuous infusion of L - -LSB- ring - ( @ ) H@ -RSB- - phenylalanine , L - -LSB- ring-@ ,@ - ( @ ) H@ -RSB- - tyrosine , and L - -LSB- @ - ( @ ) C -RSB- - leucine , and ingested @ g intrinsically L - -LSB- @ - ( @ ) C -RSB- - phenylalanine and L - -LSB- @ - ( @ ) C -RSB- - leucine labeled casein dissolved in bovine milk serum ( Cas + Serum ) or water ( Cas ) .