Associations between pre-injury racing history and tibial and humeral fractures in Australian Thoroughbred racehorses.

Long bone fractures in racehorses may present as stress fractures which have a good prognosis, or complete fractures, which often result in a fatal outcome. In order to identify differences in modifiable management practices that may contribute to these outcomes, racing histories of horses with humeral or tibial fractures and of matched controls were examined. A retrospective case-control study of Australian Thoroughbred racehorses diagnosed with a fracture of the humerus or tibia by scintigraphy or at post-mortem between 2002 and 2016 was undertaken. Control horses were matched from the same race or trial on age and sex. Statistical analysis was performed using conditional logistic regression, χ2 and Mann-Whitney U tests. More humeral fractures than tibial fractures were fatal (12/47, 26% vs. 3/35, 8.6%, P = 0.049). No differences in pre-injury racing histories were observed between cases and controls for humeral and tibial fractures. Both humeral and tibial fracture case horses were younger than the registered Thoroughbred racing population (P < 0.001), but horses sustaining humeral fractures were older than those with tibial fractures (3.3 ± 0.9 vs. 2.8 ± 0.8 years, P = 0.005) yet raced fewer times prior to the injury (0.5 ± 1.1 vs. 1.3 ± 1.7 races, P = 0.009). Horses with fatal humeral fractures were less likely to have raced than those with non-fatal humeral fractures (16.7% vs. 55.6%, P = 0.02). In conclusion, tibial and humeral fractures occur in young racehorses, and humeral fractures are more likely to be fatal in those with the least exposure to trialling and racing.

Isolation of acute-phase proteins from plasma for determination of fractional synthesis rates by a stable isotope tracer technique.

Because of the unavailability of convenient tracer methods, there is no information on the kinetic changes responsible for the increased or decreased pool sizes of the acute-phase proteins (APPs) during the metabolic response to trauma and infections. We have developed a stable isotope tracer method to measure the synthesis rates of the APPs transferrin, haptoglobin, and alpha1-antitrypsin. The proteins were isolated from plasma by either direct or sequential immunoprecipitation and purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. With the exception of haptoglobin, the major band of each protein and its standard ran to a position corresponding to its molecular mass. The major band of haptoglobin and its standard ran to a position corresponding to a molecular mass of slightly less than 44 kDa, which corresponds to the haptoglobin beta chain, molecular mass 42.5 kDa. To measure the fractional synthesis rates (FSRs) of these proteins, three children were infused with 2H3-leucine for 8 h, and the amount of 2H3-leucine incorporated into the proteins was measured by gas chromatography-mass spectrometry. The plateau isotopic enrichment of very low density lipoprotein-apoB-100-bound leucine was used to estimate the isotopic enrichment of the hepatic protein synthetic precursor pool. FSRs (%/day) of the proteins were haptoglobin, 50 +/- 8; transferrin, 19 +/- 1.1; and "alpha"1-antitrypsin, 10 +/- 1. 5.

Enteral glutamate is almost completely metabolized in first pass by the gastrointestinal tract of infant pigs.

We studied the absorption of enteral glutamate and phenylalanine using isotopic tracer and arteriovenous difference techniques. Six piglets, implanted with portal, carotid, and gastric catheters and an ultrasonic portal flow probe received a 6-h intragastric infusion of [U-13C] glutamate and [2H] phenylalanine, with a high-protein diet offered one time each hour. Amino acid concentrations and the isotopic enrichments of all mass isotopomers of glutamate, glutamine, and phenylalanine were measured in portal and arterial blood over the last hour. There was significant (P<0.025) net absorption of the indispensable amino acids as well as arginine, proline, serine, and alanine. There was no portal uptake of glutamate, aspartate, and glycine, and arterial glutamine was removed by the portal drained viscera (P<0.05). At isotopic steady state, 72% of the [2H] phenylalanine but only 5% of the [U-13C] glutamate tracer appeared in the portal blood. We conclude that, in fed infant pigs, the gut metabolizes virtually all of the enteral glutamate during absorption. Therefore, glutamate and glutamine in the body as a whole must derive almost entirely from synthesis de novo.

Fractional synthesis rates of retinol-binding protein, transthyretin, and a new peptide measured by stable isotope techniques in neonatal pigs.

Our objective was to develop a stable isotopic method to measure the synthesis rates of retinol-binding protein (RBP) and transthyretin (TTR). Both proteins were isolated from human and pig plasma by sequential immunoprecipitation and purified by SDS-polyacrylamide gel electrophoresis under denaturing conditions. Both human and pig anti-RBP precipitates contained a peptide (TTR2) that had a molecular mass that was similar but not identical to that of TTR subunit. The N-terminal amino acid sequence of porcine TTR2 was highly but not completely homologous with porcine TTR. Human TTR2 showed no homology with TTR but was completely homologous with an internal sequence of human fibrinogen alpha chain. To measure the fractional rates of synthesis (FRS) of these peptides, six infant pigs were infused with [2H3]leucine at a constant rate for 6 h, and the amount of [2H3]leucine incorporated into the proteins was measured by negative chemical ionization gas chromatography-mass spectrometry. The plateau isotope ratio of plasma very low density lipoprotein apoB-100-bound leucine was used to estimate the isotopic enrichment of hepatic protein synthetic precursor pool. The mean FRS (% h +/- S.E.) of TTR (1.97 +/- 0.13) and RBP (3.89 +/- 0.07) were significantly different. The FRS of TTR2 was low (0.31 +/- 0.19) relative to that of RBP and TTR. Thus, three different peptides with different turnover rates seem to be involved in the transport of retinol.

Mechanisms by which dichloroacetate lowers lactic acid levels: the kinetic interrelationships between lactate, pyruvate, alanine, and glucose.

Dichloroacetate (DCA) is gaining use as an alternative to bicarbonate therapy in the treatment of lactic acidosis. To determine the mechanism(s) by which DCA lowers blood lactate levels, we studied its effect on the kinetic interrelationships between pyruvate, lactate, alanine, and glucose in the hindlimb of dogs during hormonal stimulation of pyruvate production (Ra) and its conversion to lactate. Three groups of dogs (n = 6) were infused with 1-13C-pyruvate to measure whole body pyruvate Ra, and pyruvate Ra and utilization (Rd) across the hindlimb during either a 4-hr infusion of saline (controls), or somatostatin, glucagon, and epinephrine (SGE), or SGE plus dichloroacetate (SGE + DCA). Pyruvate Ra was used as an index of rate of glycolysis and Rd as an index of pyruvate oxidation. In the controls, all kinetic parameters were constant during the saline infusion. Hindlimb pyruvate Ra and Rd were almost equal, and lactate release negligible. Compared to controls, SGE administration significantly increased (P < 0.05) wholebody pyruvate Ra (48.5 +/- 6.2 vs 33.6 +/- 2.4 mumol/kg/min) and blood lactate levels (P < 0.05). Hindlimb pyruvate Ra increased by approximately 150%, but Rd remained unchanged resulting in marked increases in lactate and alanine effluxes. Adding DCA to the SGE infusion significantly reduced wholebody pyruvate Ra (P < 0.05) and blood lactate levels (P < 0.01). In the hindlimb, however, there was no decrease in lactate output, despite a 91% increase in pyruvate utilization because pyruvate Ra also increased. These results suggest that during stimulation of rate of glycolysis, DCA lowers lactate levels by reducing the overall availability of pyruvate for lactate synthesis. This is accomplished by suppressing the rate of glycolysis in tissues other than skeletal muscle and stimulating pyruvate oxidation.