The objective of this study was to examine the effects of clenbuterol administration on meat quality traits of veal. Sixteen Holstein-Friesian veal calves (male) were randomly assigned to one of four treatment groups; either control (n = 4) or clenbuterol-treated (1.6 micrograms.kg [corrected] BW-1.d-1, 42 d) with a withdrawal period between clenbuterol treatment and slaughter of 8 d (n = 4), 4 d (n = 4), or 2 d (n = 4). All animals were slaughtered at the same day at a commercial slaughterplant. At 30 min postmortem the carcasses were split and the right carcass side was electrically stimulated. After 24 h of cooling the longissimus, semimembranosus, triceps brachii, and psoas major muscles were excised and vacuum-packaged. After 1, 7, and 13 d of vacuum storage at 2 +/- 2 degrees C the muscles were sampled to determine tenderness, water-holding capacity, and color characteristics. Clenbuterol treatment resulted in a slower rate of pH decline in the unstimulated longissimus muscle but did not affect the ultimate pH. Clenbuterol treatment resulted in toughening of the longissimus, semimembranosus, and triceps brachii muscles after 1 and(or) 7 d of storage (P < .05). It is suggested that this resulted from a decrease in postmortem proteolysis because both the intensity of a 30-kDa peptide and the myofibril fragmentation index were lower in clenbuterol-treated muscles. Clenbuterol treatment resulted in increased lightness (L*-value) of longissimus and semimembranosus muscles (P < .05), coincident with a lower water-holding capacity. In a following experiment, the effect of clenbuterol administration (0 [n = 5] and 1.0 [n = 5] mg/kg of feed for 27 d) on calpain and calpastatin levels at 1 d postmortem in longissimus muscles of Friesian Pie Noire veal calves was investigated. Clenbuterol administration resulted in an increase in calpastatin levels (P < .05) and a trend (P < 0.1) toward a decrease in mu-calpain activity at 1 d postmortem.

Transfer from a low cholesterol commercial diet to a high cholesterol diet, containing 2% (wt/wt) cholesterol and 0.5% cholate, caused an increase in serum cholesterol from about 2.5 mmol/L in two inbred rat strains to 5 mmol/L in the hyporesponsive strain and to 20 mmol/L in the hyperresponsive strain. In both strains the excess of cholesterol in the serum was exclusively located in the very low density lipoproteins. Cholesterol feeding caused a sevenfold increase in the amount of cholesterol in the liver, the increase tending to be greater in the hyporesponders. On the commercial diet, the decay of specific radioactivity of serum cholesterol after the intravenous administration of labeled cholesterol was faster in the hyporesponsive rats. The rate of fecal excretion of radioactive bile acids on this diet was higher in the hyporesponders when compared with the hyperresponders, whereas there was no strain difference with regard to the output of fecal neutral steroids. Sterol balance data showed that whole-body cholesterol synthesis on the low cholesterol diet was about twofold higher in the hypo- than in the hyperresponders. When fed the high cholesterol diet the half-life in the serum of injected radioactive cholesterol was about six times shorter in the hyporesponders. In absolute amounts, the hypo- and hyperresponders excreted similar amounts of endogenous (radioactive) bile acids and fecal steroids with the feces on this diet.

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A sensitive radiochemical method for the determination of the pyruvate dehydrogenase complex (PDHC) activity in skeletal muscle tissue, based on the decarboxylation of [1-14C]-pyruvate to 14CO(2), is described. Measurements can be carried out either in muscle homogenate or in 600-g supernatant, both obtainable from a small muscle biopsy specimen (20 mg). In addition to NAD^+, thiamine pyrophosphate and coenzyme A in the incubation mixture, a preparation of NADH:cytochrome c reductase (NADHCR) together with cytochrome c has a stimulating effect on the PDHC activity. NADHCR constitutes an oxidation system for NADH to prevent feedback inhibition. Addition of L-camitine also results in stimulation of PDHC by trapping the produced acetyl-CoA as acetylcarnitine. Special care for radioactive pyruvate, with freeze drying and storage at -20 °C under nitrogen, and determination of the purity during every PDHC assay, is required. In the presented assay a K(m) value of 0.084 mmol/l was found for pyruvate. Nonsigmoidal kinetics was found with a Hill coefficient of 1.63. With the described method, a totally Mg^2+,Ca^2+-stimulated PDHC activity is measured. Addition of a purified specific pyruvate dehydrogenase phosphatase did not yield a higher PDHC activity. Finally, comparison of total PDHC activity with [1-14C]-pyruvate oxidation rates, both measured in the supernatant prepared from fresh muscle, shows an equimolar correlation, indicating that total PDHC activity is rate limiting in the assay for the pyruvate oxidation rate. Neonatal muscle exhibits five to ten times lower PDHC activities and pyruvate oxidation rates than controls (age > 3 years).

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