Abstract
Male Wistar rats (17 wks. old, body weight ∼400 g), fitted with an intra gastric cannula and with a catheter in the vena jugularis were divided into 3 groups and given a marginal ration of the feeding solution Nutrison Standard (1g protein and 350 kJ ME per day). Group 1 had ad lib. access to the drinking bottle, the groups 2 and 3 were pair fed by gastric infusion, splitted up into 2 greater meals for group 2 respectively into 6 smaller meals for group 3. After adaptation all animals get an i.p. injection of doubly labelled tracer solution (200μl) containing 2.5mg L-[15N]leucine (72 atom% 15N) combined with either [1-14C]- or [U-14C] leucine (37 kBq).
The course of 14CO2 expiration was estimated by breath test over 4h in intervals of 15 min and the course of urinary 15N excretion over 24h in intervals of 45 resp. 90 min. An infusion of saline (0.9% 5ml/h) into the vena jugularis was used to provoke sustained urine production of the animals during the experiment.
From the parameters of the excretion curves of breath 14CO2 resp. urine 15N (cumulative end value) and from the N balance the portions of leucine-C and leucine-N used for protein synthesis, transamination decarboxylation and total oxidation as well as the kinetic parameters for whole body protein metabolism were computed.
The following conclusions were drawn:
6 x feeding regime produces a small but measurable amino acid economy effect in comparison to 2 x feeding regime.
Protein gain for 2 x feeding group was significant smaller than for 6 x feeding group, though protein synthesis rate was higher, but was overcompensated by a greater increase of protein breakdown rate for the 2 x feeding group. Energy storage in form of fat and glycogen built from decarboxylation was unaffected by feeding frequency. The amount of leucine oxidized for heat production was 4% higher for the 6 x feeding group. Transamination rate for leucine was estimated to 8–15%. Absolute values for protein flux, protein synthesis and protein breakdown may be overestimated or underestimated because the metabolism of [15N] leucine does not exactly agree with that of total N; but the proportions of them and therefore also the conclusions will be true. Better results for absolute values will be obtained using a mixture of 15N labelled AA, 15N labelled protein or hydrolysate of 15N labelled protein (yeast) as the tracer source.