Clenbuterol increases muscle mass in myostatin knockout mice

Clenbuterol, a β‐2 adrenergic agonist, increases muscle and decreases adipose tissue growth; inactivation of myostatin, a TGF‐β superfamily member, in mice also increases muscle growth and reduces adiposity. It is not clear, however, whether these two effects are additive. Thus, the aim of this research was to determine responsiveness of myostatin knockout (MKO) mice to clenbuterol treatment. For two weeks, five week old male MKO and wild type (WT) mice were housed individually, fed a 24% protein, 6% fat diet and given free choice access to either tap water or tap water with 20 ppm clenbuterol (clen). Weight of mice at the end of two weeks was not affected by clen treatment, but clen did impact carcass composition. Weight of the skinned, decapitated, eviscerated carcass (empty carcass) was increased in clen treated MKO mice compared with MKO control mice (P < 0.05). This increased carcass weight is almost solely attributable to increased protein and water deposition while fat deposition was reduced. In contrast, empty carcass weight of clen treated WT mice was not different than control WT mice (P > 0.10). In WT mice clen treatment did not impact protein and fat deposition as greatly as in MKO mice. These data demonstrate that administering clen to MKO mice increases muscle mass and decreases fat deposition. MKO mice do respond, and may be more responsive than WT mice, to clen treatment.