Leucine and its catabolites alter mitogen-stimulated DNA synthesis by bovine lymphocytes

This study determined effects of leucine and its catabolites on in vitro, mitogen-stimulated DNA synthesis by bovine lymphocytes. Cultures grown in leucine-free or leucine-replete (0.4 mmol/L leucine) medium were supplemented with 0-10.0 mmol/L leucine or individual catabolites. Leucine at greater than or equal to 0.08 mmol/L was necessary for normal DNA synthesis by mitogen-stimulated bovine lymphocytes. beta-Hydroxy-beta-methylbutyrate (HMB) and beta-hydroxy-beta-methylglutarate (HMG) had minimal effect on unresponsiveness of mitogen-stimulated bovine lymphocytes in leucine-free medium; however, alpha-ketoisocaproate (KIC) at 0.4 and 2.0 mmol/L partially or completely restored DNA synthesis. In leucine-replete medium, 0.016-0.4 mmol/L KIC and 0.016-2.0 mmol/L HMB and HMG did not affect DNA synthesis. At 2.0 and 10.0 mmol/L, KIC inhibited (P less than 0.01) DNA synthesis, whereas HMB and HMG at 10.0 mmol/L enhanced (P less than 0.01) DNA synthesis. Overall, these results suggest that leucine is necessary for mitogen-induced DNA synthesis by bovine lymphocytes, and that this requirement for leucine can be partially met by KIC. When leucine was not limiting, KIC, HMB and HMG at concentrations that might occur in vivo did not alter lymphocyte DNA synthesis in vitro.