Nutrient-hormone signals regulating muscle protein turnover in pigs

Abstract

In economic terms, muscle is the most important tissue for pig producers. Research has been largely focused, therefore, on the means by which to increase carcass muscle content, as well as the efficiency of nutrient use for muscle growth. Since a major component in this tissue is protein, the rate at which protein is continuously synthesized and degraded, i.e. the rate of protein turnover, is related to growth and, particularly, to feed efficiency for growth. Thus, protein turnover is of nutritional importance. Furthermore, turnover is primarily dependent on intrinsic factors such as age, sex or genotype, which are generally related to a specific hormone status. However, most of the time, these intrinsic factors interact with nutrients either through stimulation of hormone secretion or production in an endocrine, or autocrine or paracrine way, andlor through action at the receptor level. The present paper describes some of the nutrient-hormone signals involved in the regulation of muscle protein turnover in pigs. THE NUTRITIONAL IMPORTANCE OF MUSCLE PROTEIN TURNOVER IN PIGSThe first nutritional impact of protein turnover is on energy requirement. In pigs, results of experiments published at the beginning of the 1980s can be used to estimate the proportion of heat production attributable to whole-body protein synthesis in a 35 kg growing pig. The estimate given by Reeds & Fuller (1983) was 20 % on the basis of an energy cost of 5.32kJ/g protein synthesized (Reeds et al. 1981), with a marginal increase in protein synthesis rate of 2.2g/g deposited protein (Reeds et al. 1980). The minimal value calculated for the energy cost of protein synthesis using the stoichiometric approach is 3.56 kJ/g (Waterlow et al. 1978). The difference between the theoretical and measured value was explained by auxiliary energy expenditure (Reeds et al. 1985). Indeed, Nai, KiATPase (EC 3.6.1.3)-dependent respiration was shown to be closely associated with protein synthesis rates in pig muscles (Adeola et al. 1989). However, even with the stoichiometric approach, the range of the estimates may be 3.0-7.3 M/g depending on the assumptions used (Aoyagi et al. 1988). On the basis of more recent energy metabolism studies giving a marginal cost for fat deposition of 9.7kJ/g (efficiency of energy for fat accretion 0.80) and a marginal cost for protein deposition of 15.9 M/g (efficiency of energy for protein accretion 0.60) according to Noblet et al. (1989), the highest value (7.3 kJ/g synthesized protein) can also be estimated using the measurements of Reeds et al. (1980) in pigs. It would enable the cost of additional protein synthesis associated with protein deposition to match the cost of protein deposition. That would provide an estimate of 30 % of total heat production associated with protein synthesis in a 35 kg pig, bearing in mind that about half this amount is part of the energy requirement for maintenance (Fig. 1).As far as muscle is concerned, it must be stated that due to its slow rate of protein turnover compared with liver and gas...

Effects of dietary protein quality on energy metabolism and thyroid hormone Status in growing pigs

“…In general, long term feeding of dietary proteins with a lower biological value leads to significant lower growth Performance, i.e. protein deposition, than feeding dietary proteins with a higher value (SALTER et al, 1990;ROY et al, 1997;SEVE et al, 1997). The present results indicate changes in the same manner when feeding SPI-with the lower biological value in comparison to CAS+ in all periods at both protein levels.…”

Intestinal development and growth performance of early-weaned piglets fed a low-threonine diet

“…This could be associated with a stimulation of the intestinal fractional protein synthesis rate (Sè ve et al, 1986;Ponter et al, 1994). In the same way, Sè ve and Ponter (1997) reported that an inadequate dietary threonine supply in early-weaned piglets induced an increased fractional protein synthesis rate in the duodenum probably associated with an acceleration of protein turnover.…”

“…This could be ascribed to an enhanced AA utilisation by the tissues of the LT piglets. Indeed, previous results showed that in weaned piglets, threonine deficiency increased fractional protein synthesis rate in the muscle and in the intestine (Sè ve and Ponter, 1997). Concerning non-essential AA, decrease in plasma glutamine and some of their end products (alanine, citrulline and ornithine) in LT piglets at day 4 could be in relation to the high energy cost of an increased protein turnover in the intestine since glutamine is used as a major energy fuel by the gut.…”

Maternal treatment with somatotropin during early gestation affects basic events of myogenesis in pigs

“…It has been shown that postnatal application of somatotropin clearly stimulates muscle fibre hypertrophy in pigs (Beermann et al 1990;Solomon et al 1990;Lefaucheur et al 1992;Sørensen et al 1996) and other mammalian species (Ullmann and Oldfors 1989;Ono et al 1996), but does not affect the number of muscle fibres as described for pig muscle (Rehfeldt et al 1999). Muscle fibre hypertrophy as induced by exogenous growth hormone is based mainly on increased satellite cell proliferation and muscle protein synthesis (Beermann et al 1983;Etherton and Bauman 1998) and also decreased protein degradation (Weikard et al 1992;Sève and Ponter 1997).…”