Responses in the absorptive phase in muscle and liver protein synthesis rates of growing rats.
The effect of time after beginning of a meal (30, 60, 90 and 120 min) on liver and gastrocnemius muscle protein synthesis was tested in growing male rats using the large dose technique, based on a 10 min exposure to [15N]phenylalanine. The fractional synthesis rate was estimated from the ratio between the atom percent excess of tissue protein-bound and free labelled phenylalanine. The latter was measured by gas chromatography mass spectrometry using the tertiary-butyldimethylsilyl amino acid derivatives. The protein-bound phenylalanine of gastrocnemius muscle was separated from the other amino acids using preparative amino acid chromatography and then oxidised to N2 in an automated carbon-nitrogen Roboprep (CN) combustion module attached to a continuous flow isotope ratio mass spectrometer (IRMS), with m/z ions 28 and 29 monitored. The protein-bound phenylalanine from liver was separated by a gas chromatograph attached to a sample preparation module and an isotope ratio mass spectrometer (GC C-IRMS), with again m/z ions of 28 and 29 monitored. The following results were obtained: the daily fractional protein synthesis rates (ks) in gastrocnemius muscle and liver were 13.9% and 65.6% respectively, in 12 h fasted 145 g rats. These ks increased within 30 min after ingestion of meal to 14.9% and 91.8% for muscle and liver, respectively, and remained at these values for the next 90 min (14.6% and 87.4% at 60 min, and 14.3% and 88.6% at 120 min after the beginning of feeding). It was concluded that measurement of protein synthesis rates characteristics for the absorptive phase can be undertaken in a period from thirty minutes to two hours after start of a meal, without significant changes in the ks values.
Dänicke
S
S
Institute of Animal Nutrition and Planned Crop Storage, Agricultural Faculty, Martin-Luther-University Halle-Wittenberg, Germany.
Nieto
R
R
Lobley
G E
GE
Fuller
M F
MF
Brown
D S
DS
Milne
E
E
Calder
A G
AG
Chen
S
S
Grant
I
I
Böttcher
W
W
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D004435:Eating; D007408:Intestinal Absorption; D008099:Liver / Q000378:metabolism*; D008297:Male; D013058:Mass Spectrometry; D009124:Muscle Proteins / Q000096:biosynthesis*; D018482:Muscle, Skeletal / Q000378:metabolism*; D009587:Nitrogen Isotopes; D010649:Phenylalanine / Q000378:metabolism; D014176:Protein Biosynthesis; D051381:Rats; D013997:Time Factors
D000596:Amino Acids; D009124:Muscle Proteins; D009587:Nitrogen Isotopes; D010649:Phenylalanine