The temporal relationship between glycogen phosphorylase and activation of the pyruvate dehydrogenase complex during adrenaline infusion in resting canine skeletal muscle

Creatine and creatinine contents in different diet types for dogs - effects of source and processing

The concentrations of creatine and its degradation product creatinine were determined in a variety of unprocessed as well as processed feedstuffs suitable for dogs. Unprocessed feedstuffs were categorised as single feedstuffs, bone and raw food diets (BARF), and small vertebrates, for example prey animals. Processed feedstuffs were categorised as meat/meat and bone meals, complete wet diets and complete dry diets. The feedstuffs were chosen to cover a broad range of each of the three defined processed and unprocessed feed categories available on the market without further subclustering. The creatine content of the samples was compared on a dry matter, protein and energy basis. The relation of creatine to crude protein permitted a rating of the meat quality in terms of muscle tissue.

RESULTS

We found no difference in creatine concentrations between the three categories of unprocessed feedstuffs (raw single feedstuffs, prey and BARF diets), neither on a dry matter basis nor when expressed relative to crude protein and metabolisable energy respectively. Significantly lower levels were determined in meat/meat and bone meal and commercial dry diets (e.g. 303 mg creatine/MJ ME in unprocessed vs. 6 mg/MJ ME in processed feedstuffs; p < 0.001). We conclude that in relation to ME, the exclusive use of conventionally processed diets for dogs, especially dry diets, leads to considerably lower intake of creatine which is a natural compound of the diet of this carnivorous and omnivorous species.

Muscle pyruvate availability can limit the flux, but not activation, of the pyruvate dehydrogenase complex during submaximal exercise in humans

While lowering muscle glycogen availability to an extent that would reduce muscle pyruvate formation during intense exercise, we investigated the importance of muscle pyruvate availability to pyruvate dehydrogenase complex (PDC) activation during intense exercise in human skeletal muscle. The present study demonstrated that regardless of whether pre-exercise muscle glycogen content was at a habitual resting concentration (412 +/- 30 mmol (kg dry muscle)(-1)) or depleted (60 +/- 3 mmol (kg dry muscle)(-1)), the increase in PDC activation from its resting value (5.46 +/- 0.96 and 3.67 +/- 0.34 nmol acetyl-CoA min(-1) (mg protein)(-1), respectively) during 10 min of exercise at 75% of the maximum rate of oxygen consumption (VO2max) (delta12.82 +/- 1.72 and delta13.24 +/- 1.42 nmol acetyl-CoA min(-1) (mg protein)(-1), respectively) was the same, despite pyruvate accumulation during exercise being 3-fold lower in the glycogen depleted state (delta0.34 +/- 0.04 and delta0.11 +/- 0.06 mmol (kg dry muscle)(-1), P < 0.001). However, as a result of the reduction in pyruvate availability, calculated flux through the PDC reaction was at least 2-fold lower in the glycogen depleted state compared with normal (21.81 +/- 2.62 and 9.41 +/- 0.63 nmol acetyl-CoA min(-1) (mg protein)(-1), respectively; P < 0.001). It is therefore pertinent to conclude that whilst muscle pyruvate availability appears to be important to the rate of flux through the PDC reaction during in vivo contraction, it is not of primary importance to the control of PDC activation under these conditions, which is probably principally regulated by muscle calcium availability. The proposed central role of pyruvate in muscle PDC activation during in vivo contraction may therefore have been over stated.