Influence of dietary protein and recombinant porcine somatotropin administration in young pigs: III. Muscle fiber morphology and shear force

Does intrauterine crowding affect the force generating capacity and muscle composition of the piglet front limb?

In the pig, intrauterine competition (IUC) greatly affects postnatal traits, such as birth weight, but also locomotor capacities. In a previous study, our group discovered a lower motor performance in piglets with a low birth weight and low vitality (L piglets), compared to piglets with a normal birth weight and normal vitality (N piglets). In order to explain the force deficit causing this reduced motor performance, in a subsequent study, we investigated whether this deficit in L piglets was caused by a lower force generating capacity (FGC) of the extensors of the hind limb and/or a lower number of type II (fast-twitch) fibers in m. vastus lateralis. L piglets had a lower absolute FGC, but surprisingly, a higher relative FGC (to birth weight) in the hind limb, compared to N piglets. In addition, we found no differences in fiber composition of m. vastus lateralis. In the present study, we assessed whether this higher relative FGC is a common feature for front and hind limb locomotor muscles of L piglets. To that end, the physiological cross-sectional area of the main extensor muscles of the front limb was calculated from their volume and fiber length, in order to calculate both the absolute and the relative FGC. By immunohistochemical staining of m. triceps brachii caput longum, the percentage of type II (fast-contracting) fibers could be determined. Similar to the results of the hind limb, we found a smaller absolute FGC, but a larger relative FGC in the front limb of L piglets, compared to N piglets. In addition, m. triceps brachii caput longum did not have a different muscle fiber composition in L and N piglets. As such, we can conclude that IUC affects the locomotor muscles in the front and hind limb in a similar way and that the observed force deficit in L piglets cannot be explained by a different force generating capacity or a lower percentage of type II muscle fibers.

Effects of dietary protein restriction on muscle fiber characteristics and mTORC1 pathway in the skeletal muscle of growing-finishing pigs

Background

To investigate the effects of dietary crude protein (CP) restriction on muscle fiber characteristics and key regulators related to protein deposition in skeletal muscle, a total of 18 growing-finishing pigs (62.30 ± 0.88 kg) were allotted to 3 groups and fed with the recommended adequate protein (AP, 16 % CP) diet, moderately restricted protein (MP, 13 % CP) diet and low protein (LP, 10 % CP) diet, respectively. The skeletal muscle of different locations in pigs, including longissimus dorsi muscle (LDM), psoas major muscle (PMM) and biceps femoris muscle (BFM) were collected and analyzed.

Results

Results showed that growing-finishing pigs fed the MP or AP diet improved (P < 0.01) the average daily gain and feed: gain ratio compared with those fed the LP diet, and the MP diet tended to increase (P = 0.09) the weight of LDM. Moreover, the ATP content and energy charge value were varied among muscle samples from different locations of pigs fed the reduced protein diets. We also observed that pigs fed the MP diet up-regulated (P < 0.05) muscular mRNA expression of all the selected key genes, except that myosin heavy chain (MyHC) IIb, MyHC IIx, while mRNA expression of ubiquitin ligases genes was not affected by dietary CP level. Additionally, the activation of mammalian target of rapamycin complex 1 (mTORC1) pathway was stimulated (P < 0.05) in skeletal muscle of the pigs fed the MP or AP diet compared with those fed the LP diet.

Conclusion

The results suggest that the pigs fed the MP diet could catch up to the growth performance and the LDM weight of the pigs fed the AP diet, and the underlying mechanism may be partly due to the alteration in energy status, modulation of muscle fiber characteristics and mTORC1 activation as well as its downstream effectors in skeletal muscle of different locations in growing-finishing pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s40104-016-0106-8) contains supplementary material, which is available to authorized users.

Expression of GHR and PGC-lα in association with changes of MyHC isof orm types in longissimus muscle of Erhualian and Large White pigs (Sus scrofa) during postnatal growth

Myofibre composition in longissimus dorsi (LD) muscle of Erhualian (EHL) and Large White (LW) pigs was investigated by determining the ratios of mRNA abundances of four myosin heavy chain (MyHC) isoforms (MyHC I, MyHC 2a, MyHC 2x and MyHC 2b) using multiplex RT-PCR. The relationship between expression of growth hormone receptor (GHR) and peroxisome proliferator-activated receptor α coactivator-lα (PGC-lα) mRNAs and changes ofmyofibre type composition during postnatal growth from 3 to 180 days of age were analysed. At 3 days of age, proportions of MyHC I, 2a and 2x fibres were high while only a few MyHC 2b fibres were differentiated. Dramatic changes were observed from day 3 to day 20 with significantly decreased MyHC I, 2a and 2x fibres but abrupt increases in MyHC 2b fibres in both breeds of pigs. Breed difference was exhibited only from day 90, with higher MyHC 2b but less MyHC I and 2a expression in LW pigs. Developmental pattern of GHR mRNA expression in LD muscle coincided with that of MyHC 2b, with LW pigs expressing higher abundance of GHR mRNA. PGC-lα mRNA expression followed distinct patterns in the two breeds of pigs, a higher level of PGC-lα mRNA being expressed in LD muscle of EHL pigs, the breed that possessed more oxidative fibres (MyHC I and MyHC 2a).

Muscle type-specific responses of myoD and calpain 3 expression to recombinant porcine growth hormone in the pig

Sixteen castrated male Large White × Landrace pigs were employed to investigate the muscle type-specific changes of gene expression in response to recombinant porcine growth hormone (rpGH) administration. Pigs were injected intramuscularly with rpGH (4 mg/day, n = 8) or saline (n = 8) for 28 days. Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to determine the mRNA abundance of genes related to muscle growth in longissimus dorsi (LD) and semitendinosus (ST) muscles. Myofibre-type composition was characterised by the ratio of the expression of myosin heavy chain (MyHC) 1, 2a or 2b relative to 2x. The results showed that the relative myofibre-type composition of neither LD nor ST was affected by rpGH administration. rpGH administration did not induce significant changes in the abundances of myostatin and myogenin mRNA in both types of muscle. MyoD and calpain 3 mRNA were significantly increased after rpGH treatment in ST muscle, whereas the difference was not significant in LD muscle. A tendency of down-regulation was observed for PGC-1α mRNA expression in ST muscle of rpGH-treated group (P = 0.16). These results suggest that myoD, calpain 3 and probably PGC-1α may be involved in the mechanism of exogenous GH action on skeletal muscle growth; rpGH up-regulates mRNA expression of myoD and calpain 3 in a muscle type-specific manner, being more remarkable in ST than in LD, whereas no influences of rpGH on the mRNA expression of myostatin and myogenin were detected.

The modulator effect of GH on skeletal muscle lysosomal enzymes is dietary protein dependent

OBJECTIVE

The purpose of this work is to determine whether changes in dietary protein level could alter the modulator effect that GH has on the muscle lysosomal system by influencing the hydrolytic activities of cathepsin D, acid RNase and DNase II and the participation of these enzymes in muscle growth.

DESIGN

BALB/c female mice were fed a diet containing 20% (HP) or 12% (MP) protein ad libitum and were treated with either saline (s) or rhGH (GH) (74 ng/g) for 29 days. Body weight and feed intake were recorded daily. At 25, 30, 35, 40, 45 and 50 days of age, five mice from each group were slaughtered and nucleic acids and protein concentrations and cathepsin D, acid RNase and DNase II activities in gastrocnemius muscle were analysed. Correlation coefficients were used to analyse the links between the activity of each enzyme with its substrate.

RESULTS

GH-treatment induced a depletion-recovery response in muscle growth through a compensatory mechanism. Changes in protein content, DNA and RNA concentrations were related to changes in lysosomal enzyme activities. Muscle cathepsin D activity in saline mice fell as the dietary protein concentration increased. GH-treatment reversed this effect by enhancing the proteolytic activity in muscle of well-fed mice and inhibiting it in mice fed a 12% protein diet. This inversion appears to be related to the different mechanism elicited by GH-treatment on skeletal muscle protein growth in each dietary group. An opposite trend was observed in muscle acid nuclease activities. Acid RNase and DNase II increased according to the dietary protein concentration, since a 12% protein diet induced a lower catabolism, especially on muscle DNA of saline mice. In contrast, GH-treatment decreased acid RNase and DNase II activities, but only in mice fed a 20% protein diet, perhaps leading to spare muscle RNA for protein synthesis, as well as to the inhibition of DNA degradation during catch-up growth. A lower dietary protein concentration appeared to reverse the GH protective effect on nucleic acids.

CONCLUSIONS

GH seems to act as a dietary protein-dependent modulator of the skeletal muscle lysosomal enzyme activity. These lysosomal enzymes play a role during muscle growth in GH-treated post-weaning mice by modifying muscle protein and DNA and RNA degradation.

Effects of dietary factors and other metabolic modifiers on quality and nutritional value of meat

A number of technologies that increase feed efficiency and lean tissue deposition while decreasing fat deposition have been developed in an effort to improve profitability of animal production. In general, the mode of action of these metabolic modifiers is to increase muscle deposition while often simultaneously reducing fat deposition. However, there have been some concerns that the focus on increasing production efficiency and lean meat yield has been to the detriment of meat quality. The aim of this review is to collate data on the effects of these metabolic modifiers on meat quality, and then discuss these overall effects. When data from the literature are collated and subject to meta-analyses it appears that conservative use of each of these technologies will result in a 5-10% (0.3-0.5kg) increase in shear force with a similar reduction in perception of tenderness. However, it should be borne in mind that the magnitude of these increases are similar to those observed with similar increases in carcass leanness obtained through other means (e.g. nutritional, genetic selection) and may be an inherent consequence of the production of leaner meat. To counter this, there are some other metabolic factors and dietary additives that offer some potential to improve meat quality (for example immuncastration) and it is possible that these can be used on their own or in conjunction with somatotropin, approved β-agonists, anabolic implants and CLA to maintain or improve meat quality.

The biphasic response of porcine tendon to recombinant porcine growth hormone

The purpose of this study was to investigate the effect of recombinant porcine growth hormone (rpGH) administration on the growth and maturational changes of the calcanean tendon in male pigs. Twenty-four orchidectomized crossbred (Duroc X Large White X Landrace) pigs were randomly assigned to 2 months of rpGH-treatment (2mo-rpGH), 3 months of rpGH-treatment (3mo-rpGH), or saline-treated control (Control) groups. Saline or rpGH (10mg/mL given as a constant dose throughout the experiment) was administered twice weekly via 1 mL intramuscular injections. Following the 2mo-rpGH treatment, tendon concentrations of proteoglycan (uronic acid) significantly decreased, non-reducible collagen cross-link content (HP) significantly increased, and hydroxyproline (Hyp) concentrations remained unchanged, with a concomitant significant increase in tendon DNA concentrations, suggesting an up-regulation of cell proliferation. In the 3mo-rpGH treated animals, a decrease in tendon DNA concentration, an increase in proteoglycan and hydroxyproline concentrations, as well as a decrease in HP cross-links were found, suggesting accretion and differentiation of the extracellular matrix components. These findings support the idea that calcanean tendon responds temporally to rpGH treatment, affecting both cell division and tendon metabolism. Responsiveness of the tendon collagen to rpGH may be influenced by the onset and/or the duration of the exogenous growth hormone treatment.

Distribution of monocarboxylate transporter isoforms MCT1, MCT2 and MCT4 in porcine muscles

AIM

Monocarboxylate transporters (MCT), which cotransport lactate anions and protons across cell membranes, are important for regulation of muscle pH. We measured amounts of MCT1, MCT2 and MCT4 by immunoblotting in five different porcine muscles, to study MCT-isoform distribution both in oxidative and highly glycolytic muscles.

METHODS

Samples from the longissimus dorsi, gluteus superficialis, semimembranosus, infraspinatus and masseter were taken from 18 slaughtered pigs.

RESULTS

Oxidative capacity, estimated on the basis of the activities of lactate dehydrogenase (LDH), citrate synthase (CS) and 3-OH-acyl-CoA dehydrogenase (HAD), was highest in the infraspinatus and masseter, and was very low in the gluteus, semimembranosus and longissimus dorsi. In all muscles, the amount of MCT1 was small but variable. The amount of MCT2 was more abundant in the glycolytic than in the oxidative muscles, while MCT4 was found in equal amounts in all muscles. MCT2, but not MCT4, correlated negatively with CS and HAD.

CONCLUSIONS

The results together with measured concentrations of lactate suggest that MCT2 may function as the housekeeping lactate transporter, preventing acidification especially in highly glycolytic muscles in which the capacity to oxidize lactate is low. The results also support the view that, as in other species, MCT4 would be important at high lactate concentrations that occur during stress.

Body growth and substrate partitioning for fat and protein gain in weaned BALB/c mice treated with growth hormone

Previously we have found that recombinant human growth hormone (rhGH) (GH; 74 ng g body wt.(-1)) administration to weaned BALB/c male mice (fed 12% or 20% protein diet) induced a growth lag and subsequent repletion similar to the catch-up growth process. We studied the partitioning of feed and protein intakes between adipose and protein body stores through the linear relationships among them. The non-linear relationship of protein intake with body fat gain/protein gain (FG/PG) ratio was especially adequate in determining the partitioning of substrates. rhGH induced an increase in feed and protein intake utilization for body weight gain (50%) and fat gain (75-140%) over saline; macronutrient utilization was the greatest in rhGH-treated mice fed 20% protein. However, growth recovery of rhGH mice was anomalous and protein intake was derived primarily for fat gain. Mice fed 12% protein (treated and control) also derived protein intake in preference to fat stores. Treatment and diet had a cumulative effect with the result that rhGH-treated animals fed 12% protein showed the greatest FG/PG ratio (1.6), and therefore, the lowest efficiency to gain protein. Weaning is a critical stage in mice when treating with rhGH, as this could provoke a growth lag. The study showed that a high protein level is required to surpass the rhGH-induced lag, but it is not enough to obtain an enhanced protein deposition. Feeding a 12% protein diet was even worse as mice did not improve on the growth lag and substrates were directed mainly to body fat.

Growth hormone administration produces a biphasic cellular muscle growth in weaning mice

The present study was undertaken to elucidate the effect of the exogenous administration of rhGH on the time course of the cellular muscle growth in male and female BALB/c mice fed 20% dietary protein between weaning and 50 days of age. Also, the efficiency of utilization of protein and energy intake to muscle DNA content and protein per cell (protein to DNA ratio) storage were studied. 120 weaned mice (21 d) were assigned to four groups based on rhGH-treatment (rhGH-treated: 7.4 ng x g(-1) BW and control: saline vehicle; via s.c. every two days) and gender. Feed intake was measured daily. At 25, 30, 35, 40, 45 and 50 days of age twenty mice were killed by cervical dislocation and the samples of gastrocnemius muscles were isolated, weighed and protein and DNA contents were measured. The rhGH administration caused a biphasic response altering the muscle cellular growth as a consequence of age-specific feed intake changes. The GH-induced fall of feed intake between 25 and 30 days of age caused decreases in muscle weight and myonuclei number (DNA), whereas muscle cell size was maintained. Later on, the self-controlled increase of feed intake led to the muscle weight recovery to control level, in spite of the irreversible DNA fall, as a consequence of the increase of cellular protein deposition and an enhancement of utilization of protein and energy intakes to deposit protein per cell. These results demonstrate that in spite of the initial (25-30 d of age) muscle DNA fall, rhGH-administration from weaning ensures the recovery of cellular muscle growth to control level through a compensatory muscle hypertrophy.

Feed intake and protein skeletal muscle in growing mice treated with growth hormone: time course effects

The exogenous recombinant human growth hormone (rhGH) administration on gastrocnemius muscle growth performance and its contribution to body growth of male and female BALB/c mice fed a 12 % protein diet from 25 to 50 days of age, as well as the mechanism of utilization of feed intake to the lean muscle deposition were studied. Male and female weaning mice (21 days of age) were injected subcutaneously for 29 days with rhGH (74 ng x g(-1)) or saline vehicle (control). Feed intake and body weight (BW) were measured daily. At 25, 30, 35, 40, 45 and 50 days of age twenty mice were killed by cervical dislocation and the gastrocnemius muscle was isolated, weighed and the protein content was measured. The rhGH administration caused a biphasic response of BW and muscle growth as a consequence of age-specific feed intake changes. The initial feed intake fall induced the allometric proportion decreases in both muscle growth versus body growth and protein muscle versus muscle growth. That effect was due to ineffient utilization of energy and protein intake on protein muscle store. Later on, the self-controlled increase of feed intake leads to the recovery of muscle weight to control values, through nutrient partitioning toward non protein tissue showing a compensatory muscle growth. This suggests that a higher dietary protein level should be necessary for promoting the protein anabolic effect of GH during weaning.

New insights into the mechanism and actions of growth hormone (GH) in poultry

Despite well documented anabolic effects of GH in mammals, a clear demonstration of such responses in domestic poultry is lacking. Recently, comprehensive dose-response studies of GH have been conducted in broilers during late post-hatch development (8 to 9 weeks of age). GH reduced feed intake (FI) and body weight gain in a dose-dependent manner, whereas birds pair-fed to the level of voluntary FI of GH-infused birds did not differ from controls. The reduction in voluntary FI may involve centrally mediated mechanisms, as hypothalamic neuropeptide Y protein and mRNA were reduced with GH, coincident with the maximal depression in FI. Growth of breast muscle was also reduced in a dose-dependent manner. Circulating IGF-I was not enhanced by GH, despite evidence that early events in the GH signaling pathway were intact. A GH dose-dependent increase in circulating 3,3',5-triiodothyronine(T3) paralleled decreases in hepatic 5D-III monodeiodinase activity, whereas 5'D-I activity was not altered. This confirms that a marked hyperthyroid response to GH occurs in late posthatch chickens, resulting from a decrease in the degradative pathway of T3 metabolism. This secondary hyperthyroidism would account for the decreased skeletal muscle mass (52) and lack of enhanced IGF-I (53) in GH-treated birds. Based upon these studies, it is now evident that GH does in fact have significant effects in poultry, but metabolic responses may confound the anabolic potential of the hormone.

Absence of growth hormone-induced avian muscle growth in vivo

Growth hormone (GH) clearly has the potential to dramatically enhance skeletal muscle accretion in red meat animals such as swine. It is generally accepted that this anabolic effect is mediated by insulin-like growth factor-I (IGF-I), a potent stimulator of proliferation and differentiation of satellite cells that are important for myofiber hypertrophy and for regeneration in postnatal muscle tissue. All available evidence suggests that the capacity for IGF-I-mediated actions of GH on avian myogenic cells is intact, and recent evidence is accumulating that GH may even have direct effects on avian skeletal muscle satellite cell proliferation and differentiation. However, with little exception, exogenous GH does not improve skeletal muscle mass, carcass protein, or any measure of muscle anabolism in domestic poultry. A primary lesion would appear to be the inability of GH to induce significant increases in circulating IGF-I concentrations in sexually immature, growing poultry. This is the case despite clear evidence of GH binding to hepatic receptors, GH-induced tyrosine phosphorylation of Janus kinase 2 (JAK2), and GH-induced expression of hepatic IGF-I mRNA and protein. Factors that should be explored with respect to this apparent discrepancy are discussed, including the regulation of IGF-I release, uptake, and interaction with cell-associated IGF binding proteins or receptors. In addition to its growth-promoting effects via IGF-I, GH has direct metabolic effects that are expressed as changes in circulating regulatory hormone and metabolite concentrations. The possibility that such changes may influence IGF-I release and action is also proposed.

Biology of somatotropin in growth and lactation of domestic animals

Impressive progress has been made during the past 15 years in our understanding of the biology of somatotropin (ST) in domestic animals. In part, this progress was sparked by advances in biotechnology that made feasible the production of large quantities of recombinant bovine ST (bST) and porcine ST (pST). The availability of recombinant bST and pST resulted in an exponential increase in investigations that explored their role in growth and lactation biology, as well as evaluated their potential for commercial use. Collectively, these studies established that administration of bST to lactating dairy cows increased milk yield, and treatment of growing pigs with pST markedly stimulated muscle growth and reduced fat deposition. In addition to these "efficacy" studies, a substantial number of investigations examined the mechanisms by which ST affects lactation and growth of domestic animals. This review summarizes the diverse physiological effects ST has on growth and lactation and discusses the underlying mechanisms that mediate these effects in domestic animals.