The aim of the present study was to investigate changes in the activity of branched-chain a-keto acid dehydrogenase (BCKAD) in skeletal muscle and the heart during brief and prolonged starvation. Fed control rats and rats starved for 2, 4 and 6 days were anesthetized with pentobarbital sodium before heart and hindlimb muscles were frozen in situ by liquid nitrogen. Basal (an estimate of in vivo activity) and total (an estimate of enzyme amount) BCKAD activities were determined by measuring the release of 14CO2 from a-keto[1-14C]isocaproate. The activity state of BCKAD complex was calculated as basal activity in percentages of total activity. Both basal and total activities and the activity state of the BCKAD were lower in skeletal muscles than in the heart. In both tissues, starvation for 2 or 4 days caused a decrease in the basal activity and activity state of BCKAD. On the contrary, in the heart and muscles of animals starved for 6 days a marked increase in basal activity and activity state of BCKAD was observed. The total BCKAD activity was increasing gradually during starvation both in muscles and the heart. The increase was significant in muscles on the 4th and 6th day of starvation. The demonstrated changes in BCKAD activity indicate significant alterations in branched-chain amino acid (BCAA) and protein metabolism during starvation. The decreased BCKAD activity in skeletal muscle and heart observed on the 2nd and 4th day of starvation prevents the loss of essential BCAA and is an important factor involved in protein sparing. The increased activity of BCKAD on the 6th day of starvation indicates activated oxidation of BCAA and accelerated protein breakdown., M. Holeček., and Obsahuje bibliografii
Beta-hydroxy-beta-methylbutyrate (HMB) is a leucine metabolite with protein anabolic effects. Since HMB is synthesized in the liver, unique effects of exogenous HMB intake may be hypothesized in subjects with liver disease, in which muscle wasting is frequently found. We studied effects of HMB on the liver and soleus (SOL) and extensor digitorum longus (EDL) muscles in partially-hepatectomized (PH) rats. HMB or saline was infused using osmotic pumps to PH or sham-operated rats for 7 days. We found lower body weight and protein content in EDL of PH rats treated with saline than in sham-operated animals. These effects were insignificant in HMB treated animals. In blood plasma of PH rats treated with HMB we found lower concentrations of creatinine and higher concentrations of urea and branched-chain amino acids (BCAA; valine, leucine, and isoleucine) than in PH animals treated with saline. HMB increased BCAA concentrations in SOL and EDL of PH animals and decreased proteolysis in EDL of both sham-operated and PH animals. In the livers of PH rats treated with HMB we found higher DNA content, DNA fragmentation, and BCAA concentrations than in saline-treated animals. The results indicate that HMB affects metabolism of BCAA and has positive influence on protein balance in muscles. Further studies are needed to clarify the effect of HMB on liver regeneration., M. Holeček, M. Vodeničarovová., and Obsahuje bibliografii
Parameters of branched-chain amino acids (BCAA; leucine, isoleucine and valine) and protein metabolism were evaluated using L-[1-14C]leucine and a-keto[1-14C]isocaproate (KIC) in the whole body and in isolated perfused liver (IPL) of rats fed ad libitum or starved for 3 days. Starvation caused a significant increase in plasma BCAA levels and a decrease in leucine appearance from proteolysis, leucine incorporation into body proteins, leucine oxidation, leucine-oxidized fraction, and leucine clearance. Protein synthesis decreased significantly in skeletal muscle and the liver. There were no significant differences in leucine and KIC oxidation by IPL. In starved animals, a significant increase in net release of BCAA and tyrosine by IPL was observed, while the effect on other amino acids was non-significant. We conclude that the protein-sparing phase of uncomplicated starvation is associated with decreased whole-body proteolysis, protein synthesis, branched-chain amino acid (BCAA) oxidation, and BCAA clearance. The increase in plasma BCAA levels in starved animals results in part from decreased BCAA catabolism, particularly in heart and skeletal muscles, and from a net release of BCAA by the hepatic tissue., M. Holeček, L. Šprongl, I. Tilšer., and Obsahuje bibliografii