Effect of the beta-adrenoceptor agonist BRL-35135 on development of obesity in suckling Zucker (fa/fa) rats.

This study was undertaken to determine whether administration of a thermogenic beta-agonist drug to Zucker fatty rats could correct some of the earliest metabolic defects detectable in brown adipose tissue (BAT). Fa/fa and fa/fa littermates were given oral administration of BRL-35135 from 8 to 16 days of age. In fa/fa rats, the lipid content of white and brown adipose tissues was significantly reduced. In the BAT of fa/fa rats, thermogenic capacity was restored to the level observed in Fa/fa rats, whereas hyperactivity of fatty acid synthetase was abolished, and a deficit in lipoprotein lipase (activity and mRNA) was partly corrected. Hyperinsulinemia in fa/fa pups was significantly reduced. The decreased content of GLUT-4 mRNA that characterized BAT of fa/fa pups was also restored to normal. At variance with observations in preobese rats, BRL had very little or no effect on lean Fa/fa rats. The present study reveals that chronic administration of a beta-agonist drug early in life prevents emergence of most of the metabolic abnormalities that characterize fa/fa rats at the onset of obesity. This suggests that impaired sympathetic activity may play a role in the development of this genetic obesity.