Clenbuterol-induced Muscle Growth: Investigation of Possible Mediation by Insulin

Am J Physiol. 1987 Oct;253(4 Pt 1):E370-5. doi: 10.1152/ajpendo.1987.253.4.E370.


The role of insulin as a possible mediator of the beta-adrenergic agonist stimulation of muscle growth was investigated. To exclude possible action of the beta-agonist on the pancreatic release of insulin, diabetes was induced in rats by a streptozotocin injection (100 mg/kg). Insulin levels were almost not detectable in these rats. Feeding either normal diet or diet containing the beta-adrenergic agonist clenbuterol (10 parts/million) did not alter plasma insulin concentrations. The effects of clenbuterol on muscle and weight gain were determined in diabetic rats given daily insulin replacement (D + I) and fed either a normal diet or clenbuterol-treated diet. Clenbuterol, fed for 1 wk, increased the wet weight of the gastrocnemius, soleus, and extensor digitorum longus muscles (15-23%) in both normal and D + I rats. Although clenbuterol increased body weight gain, it did not alter feed consumption and, therefore, feed efficiency (g gain/g food) was improved. Activities of cathepsin B and N-acetyl-beta-glucosaminidase, but not cathepsin D, were elevated in the soleus muscles of clenbuterol-treated rats. The clenbuterol-induced increase in muscle growth in the insulin-replaced diabetic rats indicated that this beta-adrenergic agonist effect was not mediated by an alteration of circulating levels of insulin, secondary to beta-agonist action on pancreatic insulin release.

MeSH terms

  • Acetylglucosaminidase / metabolism
  • Animals
  • Blood Glucose / metabolism
  • Body Weight
  • Cathepsin B / metabolism
  • Clenbuterol / pharmacology*
  • Eating
  • Ethanolamines / pharmacology*
  • Insulin / blood*
  • Male
  • Muscle Development*
  • Muscles / enzymology
  • Rats
  • Rats, Inbred Strains


  • Blood Glucose
  • Ethanolamines
  • Insulin
  • Acetylglucosaminidase
  • Cathepsin B
  • Clenbuterol