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Melengestrol acetate alters muscle cell proliferation in heifers and steers¹

Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506

² Corresponding author: cdr3{at}ksu.edu

In vitro experiments were performed to investigate the effects of melengestrol acetate (MGA) or progesterone (P4) on bovine muscle satellite cells and C₂C₁₂ myoblasts. Addition of MGA at physiological and supraphysiological concentrations resulted in a dose-dependent decrease (P < 0.05) in DNA synthesis as measured by ³H]-thymidine incorporation (TI). Similarly, P4 addition (0.01 nM) reduced (P < 0.05) TI. Addition of MGA (10 nM) increased (P < 0.05) IGF-I mRNA abundance but did not affect myogenin mRNA. Progesterone addition (10 nM) increased myogenin mRNA abundance (P < 0.05). In C₂C₁₂ cultures, P4 addition resulted in a dose-dependent decrease in TI. The antiprogestin RU486, in combination with MGA or P4, also resulted in reduced (P < 0.05) TI. Treatment with RU486 alone had a negative effect (P < 0.05) on TI that was similar to the progestins. Treatment of C₂C₁₂ myoblasts with MGA (100 nM) resulted in an increase (P < 0.05) in myogenin mRNA. These studies suggest that progestins may reduce satellite cell proliferation, ultimately affecting carcass composition.

Key Words: bovine • carcass • insulin-like growth factor-I • melengestrol acetate • progesterone • satellite cell

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