How do Beta 2 Antagonists promote hypertrophy?
by Karl Hoffman It’s been well established that beta 2 agonists promote hypertrophy of skeletal muscle in animals. There is also limited data that beta 2 agonists such as clenbuterol and albuterol are both anabolic and ergogenic in humans. What is the mechanism behind the anabolic effect of such agents? As depicted in the diagram below, beta 2 agonists bind to a cell surface receptor and initiate a signaling cascade that results ultimately in a metabolic response. One step in the signaling process involves increasing levels of the so-called second messenger cAMP (cyclic adenosine monophosphate). cAMP in turn activates so-called protein kinases. These enzymes add a phosphate group to various compounds. In some cases the added phosphate group activates the compound; in other cases phosphorylation results in deactivation of a compound. Fig 1. Beta agonists elevate cAMP, activating calpastatin and inhibiting calpain Skeletal muscle proteins are degraded via several pathways in the body. On
