Increased body-weight gain and body protein in castrated and adrenalectomized rats treated with clenbuterol.

1. Daily injection of the beta 2-adrenergic agonist clenbuterol (1 mg/kg body-weight) increased weight gain by 12% in young (35 d) male rats and by 18% in castrated rats, but had no effect on energy intake, expenditure or efficiency in either group. 2. Body fat content was not affected by clenbuterol or castration, but water and protein content were significantly increased by clenbuterol treatment in both intact and castrated rats. The ratio, body protein: fat was increased by 13 and 16% in these two groups compared with their respective, untreated controls. 3. Bilateral surgical adrenalectomy (ADX) of young (45 d) male rats significantly reduced body-weight, and energy intake, expenditure and efficiency. Carcass energy and fat contents were also reduced in ADX rats compared with age-matched controls. 4. Clenbuterol injections stimulated weight gain (% increase:intact 15, ADX 35), and increased body protein content (% increase:intact 12, ADX 8) and the ratio, carcass protein:fat (% increase:intact 34, ADX 23). 5. These findings demonstrate that the effects of clenbuterol on body-weight gain and composition in male rats occur in the absence of either gonadal or adrenal hormones. Together with other studies, these results provide further evidence to suggest that clenbuterol probably exerts its effects by a direct action on lean body mass.