The effect of pre-treatment with various drugs on post-mortem glycolysis and the onset of rigor mortis in rabbit skeletal muscle

Association of blood glucose, blood lactate, serum cortisol levels, muscle metabolites, muscle fiber type composition, and pork quality traits

The objective of this study was to investigate the relationship of blood glucose levels with blood lactate, serum cortisol levels, postmortem muscle glycogen and lactate content, muscle fiber type composition, and pork quality traits. Compared to pigs with lower blood glucose levels, pigs with higher blood glucose levels showed higher blood lactate and serum cortisol levels at exsanguination, and they had lower residual glycogen and higher lactate content in the muscle at 45min postmortem. In addition, pigs with higher blood glucose levels had higher type IIB and lower type I area composition and finally exhibited lower muscle pH, paler color, and excessive loss of fluid on surface. These results imply that measuring blood glucose levels at exsanguination can be useful to indicate early glycolytic rates during postmortem and thus may be of value in the identification of pork with undesirable quality traits.

Dynamic high-resolution 1H and 31P NMR spectroscopy and 1H T2 measurements in postmortem rabbit muscles using slow magic angle spinning

Postmortem changes in rabbit muscle tissue with different glycogen status (normal vs low) were followed continuously from 13 min postmortem until 8 h postmortem and again 20 h postmortem using simultaneous magic angle spinning (1)H and (31)P NMR spectroscopy together with measurement of the transverse relaxation time, T(2), of the muscle water. The (1)H metabolite spectra were measured using the phase-altered spinning sidebands (PASS) technique at a spinning rate of 40 Hz. pH values calculated from the (31)P NMR spectra using the chemical shifts of the C-6 line of histidine in the (1)H spectra and the chemical shifts of inorganic phosphate in the (31)P spectra confirmed the different muscle glycogen status in the tissues. High-resolution (1)H spectra obtained from the PASS technique revealed the presence of a new resonance line at approximately 6.8 ppm during the postmortem period, which were absent in muscles with low muscle glycogen content. This new resonance line may originate from the aminoprotons in creatine, and its appearance may be a result of a pH effect on the exchange rate between the amino and the water protons and thereby the NMR visibility. Alternatively, the new resonance line may originate from the aromatic protons in tyrosine, and its appearance may be a result of a pH-induced protein unfolding exposing hydrophobic amino acid residues to the aqueous environment. Further studies are needed to evaluate these hypotheses. Finally, distributed analysis of the water T(2) relaxation data revealed three relaxation populations and an increase in the population believed to reflect extramyofibrillar water through the postmortem period. This increase was significantly reduced (p < 0.0001) in samples from animals with low muscle glycogen content, indicating that the pH is controlling the extent of postmortem expulsion of water from myofibrillar structures. The significance of the postmortem increase in the amount extramyofibrillar water on the water-holding capacity was verified by centrifugation, which showed a reduced centrifugation loss in muscles with low preslaughter glycogen status (0.9 vs 1.9%, p = 0.07).

Field gradient CPMG applied on postmortem muscles

As a new approach, Carr-Purcell-Meiboom-Gill (CPMG) experiments were performed in vitro on porcine muscles (n = 10) during the period from 15 min to 85 min postmortem and again at 24 h postmortem in the absence (G = 0) and the presence of an external field gradient (G = 0.5*10(-3) T/m), which was applied throughout the CPMG sequence. The experiments were performed on low-field nuclear magnetic resonance (NMR) equipment (0.47 T). Due to the inclusion of different pre-slaughter treatments (adrenaline treatment and pre-slaughter exercise/electrical stunning), the muscles could be divided into (I) a group (n = 5) characterized by a reduced decrease in pH postmortem and a high water-holding capacity and (II) a group (n = 5) characterized by an increased rate of pH decrease postmortem and a low water-holding capacity. Distributed analysis of the CPMG data revealed two major relaxation populations with relaxation times about 30-40 and 200-500 ms, respectively, and comparison of data obtained with G = 0 and G = 0.5*10(-3) T/m revealed effects of the external gradient on the relaxation time of both the two relaxation populations, which implies that both diffusion and relaxation contributes to the relaxation of the two populations. At 24 h postmortem the effect of the external field gradient on the relaxation time was significantly affected by muscle group (I vs. II), which reveals local differences in water diffusion in the two meat qualities. Finally, the discriminatory power with regard to muscle group (I vs. II) was investigated for data acquired with G = 0 and G = F = 0.5*10(-3) T/m, and both the two types of data were found highly suitable for separation of muscles according to meat quality.

pH Dependence of the progression in NMR T(2) relaxation times in post-mortem muscle

Continuous NMR T(2) relaxation measurements were carried out on seven rabbit longissimus muscle samples in the period from 25 min to 28 h post-mortem at 200 MHz for (1)H. To display differences in post-mortem pH progress and extent of changes in water characteristics during conversion of muscle to meat, three of the seven animals were pre-slaughter injected with adrenaline (0.5 mg/kg live weight 4 h before sacrifice) to differentiate muscle glycogen stores at the time of slaughter. Distributed analysis of T(2) data displayed clear differences in the characteristics of the various transverse relaxation components dependent on progress in pH, as did the water-holding capacity of samples 24 h post-mortem. This reveals a pronounced effect of the progressive change in pH on the subsequent development in physical/chemical states of water during the conversion of muscle to meat. Finally, the relaxation characteristics are discussed in relation to supposed post-mortem processes of protein denaturation.

Effect of type of aviary, manure and litter handling on the emission kinetics of ammonia from layer houses

1. An experiment with laying hens of 16 to 36 weeks of age was carried out to investigate differences in ammonia emission between 3 commercially available aviary housing systems and the additional effect of manure and litter handling. 2. Ammonia emission from Tiered Wire Floor (TWF), Natura and Boleg aviary systems increased rapidly from placement of the hens to a peak at 20 weeks of age and showed respective equilibrium level at 11.55, 11.24 (N.S. compared to TWF) and 14.55 (P < 0.001 compared to TWF) mg ammonia per h per hen. 3. Emission increased by 5.6% on the first day and 11% on subsequent days after removal of the manure on the belts. The litter layer increased up to about 7 cm; removal of 6.5 cm reduced emission by 20%. 4. Ammonia concentrations varied between 1 and 16 ppm, while ventilation rates were between 1 and 4 m3/h per hen to maintain inside temperature at about 22 degrees C. 5. About 82% of the droppings produced by the hens was found on the belts, either directly deposited there, or put there as litter material. The composition of the manure on the belts and the litter, a sand-droppings mixture, changed significantly during the first part of the laying cycle and differences were found between the 3 aviary systems with respect to the DM, pH, ash, Nkjeldahl and Total Ammoniacal Nitrogen concentration. 6. The changes in time and differences between the 3 systems in ammonia emissions and manure and litter composition were related to design of the systems, behaviour of the hens and degradation (of nitrogenous components) and volatilisation processes (water and ammonia).

Distinct but nonadditive effects of epinephrine and cortisol on determinants of glucose tolerance in dogs

Effects of physiological increments of epinephrine (Epi) and cortisol (F) on glucose metabolism were assessed in dogs just before and during an intravenous glucose tolerance test performed in the last 3 h of an acute (short F + Epi, 4 h F and 3.5 h Epi) or prolonged (long F + Epi, 75 h F and Epi) infusion period. Comparison of the F + Epi effects with those of F and Epi alone enabled us to describe interactions between these hormones. The increase in plasma glucose after long F + Epi [from control (saline, Sal) of 5.2 +/- 0.1 to 5.8 +/- 0.1 mmol/l; n = 8; P less than 0.01] was not greater than the sum of the glucose increments after long F and long Epi individually. Long Epi and long F both reduced glucose tolerance (KGlc) significantly, but the decline during long F + Epi (from Sal 3.6 +/- 0.7 to 2.9 +/- 0.5%/min; P greater than 0.1) was less than during either individual infusion. Minimal model analysis showed that F attenuated the inhibitory effects of long Epi on glucose-mediated glucose disposal (SGlc), so that it was not reduced from 3.8 +/- 0.8 (Sal) during long F + Epi compared with the fall to 1.3 +/- 0.7 x 10(-2) min-1 (n = 6; P less than 0.05) during long Epi alone. F had the dominant influence on insulin sensitivity (SI) during infusion of F + Epi. The reduction of SI from 8.4 +/- 1.1 (Sal) to 6.6 +/- 1.2 (short F + Epi) and 5.1 +/- 1.1 x 10(-4) min-1 per mU/l (long F + Epi; P less than 0.05) paralleled that seen with F alone but contrasted with the acute reduction of SI during short Epi (4.8 +/- 1.5; P less than 0.02 vs. Sal) and its restoration to control values of 9.0 +/- 2.1 x 10(-4) min-1 per mU/l during long Epi. We conclude that Epi and F have distinct but nonadditive effects on determinants of glucose tolerance.

The Meyerhof quotient and the synthesis of glycogen from lactate in frog and rabbit muscle

1. The conversion of lactate into glycogen was demonstrated in frog sartorius muscle in oxygen. The rates and amounts are highest when lactate is added to the bathing medium and are dependent on lactate and CO(2) concentration, as well as pH. The glycogen content of a resting muscle can be doubled in 4h at 24 degrees C. 2. Sartorius muscle, recovering aerobically in liquid paraffin from a period of anoxia, converts preformed lactate into glycogen at a lower rate and in smaller amounts than when lactate is added in an aqueous medium. The lower rates are similar to those Meyerhof found under the same conditions, after correction for temperature; they can be attributed partly to low muscle pH and partly to the limited amounts of lactate present. 3. Rabbit psoas muscle also shows the ability to convert added lactate into glycogen under aerobic conditions. The rates are low and similar to those in frog sartorius muscle recovering from anoxia. 4. The present experiments yield a Meyerhof quotient of 6.2, compared with Meyerhof's value of 4-5. However, these values are not significantly different from one another. 5. It is suggested that the glycogen coefficient, i.e. mol of glycogen formed/mol of lactate disappearing, is a more reliable way of assessing the resynthetic mechanism than the original quotient, i.e. mol of lactate disappearing/mol of lactate oxidized. The found coefficient is 0.419+/-0.024.