Evaluation of beta(2)-adrenergic agonists repartitioning effects in the rat by a non-destructive method

The beta(2)-adrenergic agonists cimaterol and clenbuterol were fed at a dose of 10 mg/kg feed to male albino rats, during a 30-day treatment study, to establish the kinetics for body weight, body fat and lean mass. Body-fat and lean-mass determinations were carried out with a non-destructive EM-Scan body composition analyser. Measurements were performed at the beginning of the study, and then at days 3, 6, 9, 12, 16, 20, 24, and 30. At the end of the observation period, plasma glucose, urea, lactate, and triglyceride concentrations, and visceral weights, were determined. An increase in body weight was observed throughout the study for all experimental groups. Body weight curves for the treated groups had steeper curve slopes than those for the control group. The curves began to level off around treatment day 16. At the end of the study, body weight gains for both treated groups were significantly higher (p less than or equal to 0.05) than those for the control groups. Feed efficiency was highly improved with both agonists. Body-fat and lean-mass kinetics developed similarly in the treated groups. The profiles for lean-mass kinetics in the experimental groups were in agreement with the respective profiles for body-weight kinetics, The body-fat and lean-mass curves for both treated groups also levelled off around treatment day 16. Final body-far decreases and lean-mass increases for cimaterol and clenbuterol treatments were significantly different (p less than or equal to 0.05) from the control group. Clenbuterol was slightly more potent than cimaterol. The attenuation in the kinetic curves for both test compounds could be a result of the downregulation of the beta-adrenoceptors. The variations seen in plasma glucose and triglyceride concentrations appeared to be a direct result of the metabolism of the beta-adrenergic agonists. Both cimaterol and clenbuterol increased heart weight and decreased weights of the other viscera. No toxic symptoms could be seen in this trial.