The effect of intake on protein metabolism across splanchnic tissues in growing beef steers

Abstract

The contribution of the total splanchnic tissue (TSP; portal-drained viscera (PDV) plus liver) to whole-body protein metabolism was estimated in relation to intake (0·6, 1·0 and 1·6 × maintenance requirements), in six multicatheterized growing beef steers used in a double 3 × 3 Latin square design. At the end of each 21 d experimental period, [1-13C]leucine was infused into a jugular vein (1·05 mmol/h for 5 h, preceded by a priming dose of 1·05 mmol). Arterial, portal and hepatic blood samples were collected hourly during the infusion. The increment in TSP leucine irreversible loss rate (ILR) observed with increasing intake reached significance (P< 0·10) only for PDV, while whole-body ILR increased markedly (P< 0·001) with intake. The relative contribution of TSP to whole-body leucine ILR averaged 44 % (25 % from PDV and 19 % from the liver). Although these proportions were not affected by intake, on an incremental basis more than 70 % of the increase of whole-body leucine ILR between the 0·6 and 1·0 × maintenance originated from the changes in TSP ILR, while the corresponding value was below 13 % between 1·0 and 1·6 × maintenance. Total whole-body leucine oxidation and fractional oxidation increased (P< 0·05) with intake. Protein retention increased with intake (P< 0·01), as a result of a greater increase in protein synthesis compared with protein degradation. Protein breakdown had a major impact on protein turnover as 65 % of the protein synthesized was degraded when intake varied from 1·0 to 1·6 × maintenance. Net leucine portal absorption increased (P< 0·001) with intake and represented 1, 16 and 23 % of whole body leucine ILR, for 0·6, 1·0 and 1·6 × maintenance, respectively. Although leucine oxidation was not a major component of whole body ILR (9·3–19·9 %), it represented 69 % of the net available leucine (portal absorption) even at 1·6 × maintenance. The lower relative contribution of the TSP to whole-body leucine ILR at higher intake indicates the proportional increase in the metabolic activity of peripheral tissues as the animals moved into positive protein balance.

Nitrogen- and energy-imbalanced diets affect hepatic protein synthesis and gluconeogenesis differently in growing lambs1,2

“…Given the importance of the liver in AA utilization and ureagenesis, it is most probably involved in the variations in the efficiency of N utilization in this study. Decreased growth and protein net retention in the LN and LE diets were also observed, similar to what was previously shown after a reduction of the amount of intake or energy intake (Calloway, 1975;Lapierre et al, 1999;Kraft et al, 2008). Concerning the impact of a decreased supply of N in the diet, either reduced N retention is observed (Bruckental et al, 1997, this study) or N retention is unaltered (Calloway, 1975;Castillo et al, 2001; Table 3.…”

The effect of the source of nitrogen supplementation on nitrogen balance, rates of plasma leucine turnover, protein synthesis and degradation in sheep

“…Whole body protein synthesis was close to those reported in sheep using the same experimental methods (Krishnamurti and Janssens 1988;Sano et al 2004), and was also similar to those in goats using the [ 2 H 5 ]phenylalanine model ). However, WBPS in sheep was considerably lower than growing steers (Lapierre et al 1999), even when the data was compared based on the metabolic body size. Sano et al (2004) reported that in sheep WBPS and WBPD were changed toward reduction with increased CP intake using both enrichments of plasma [1-13 C]Leu and a-[1-13 C]KIC.…”

Long‐chain omega‐3 fatty acids regulate bovine whole‐body protein metabolism by promoting muscle insulin signalling to the Akt–mTOR–S6K1 pathway and insulin sensitivity

“…Hyperinsulinaemic–euglycaemic–euaminoacidaemic clamp procedure Clamps were performed during steady feeding conditions achieved through 98% restricted 2 h feeding (Lapierre et al 1999; Thivierge et al 2002 b ). Hyperinsulinaemic – euglycaemic – euaminoacidaemic clamps were conducted according to the procedures described by Wray‐Cahen et al (1997).…”

“…Fed steady‐state whole‐body amino acid tracer kinetics followed by muscle biopsies l ‐[1‐ 13 C]Phenylalanine kinetics were conducted during steady nutritional intake of nutrients achieved through 98% restricted 2 h feedings (Lapierre et al 1999). The kinetics data are independent from those of the clamp and expand the response to LC n –3PUFA to a feeding‐induced stimulation.…”

“…The kinetics data are independent from those of the clamp and expand the response to LC n –3PUFA to a feeding‐induced stimulation. A minimum of 48 h separated the amino acid tracer and the bicarbonate infusion studies enabling the measure of both whole‐body flux and oxidation using stable isotopes in large animals (Lapierre et al 1999). Each measurement was conducted either before or after the other, always respecting the 48 h minimal delay.…”