EFFECT OF SOMATOTROPIN AND FEED RESTRICTION ON BODY-COMPOSITION AND ADIPOSE METABOLISM IN OBESE ZUCKER RATS

The objective of the present study was to determine whether exogenous somatotropin (STH) administration in conjunction with feed restriction could alter the composition of gain in the obese rat. Five-week-old f emale lean and obese Zucker rats were assigned to the following treatm ents for 6 wk: ad libitum fed (AL), restricted (similar to 75% of AL l ean), and restricted with STH (2 mg STH/day). Growth rate was decrease d in restricted groups and was normalized to that of the AL lean group in restricted rats treated with STH. In lean rats, restriction decrea sed protein accretion. Restriction plus STH treatment decreased lipid accretion but increased protein accretion and body weight gain compare d with the AL lean group. As expected, feed restriction reduced body s ize in obese rats, but carcass lipid was maintained at 44%, a level si milar to that of the AL obese rats. Lipid accretion rate was decreased with restriction in obese rats and was further reduced, to a level si milar to that of the lean group, in the obese rats that were restricte d and treated with STH. Protein accretion was decreased in the restric ted obese group but was normalized in those treated with STH to a leve l similar to that in the AL lean group. Basal rates of lipolysis in is olated adipocytes were not affected by STH. However, STH treatment nor malized the responsiveness of cells from the obese rats to stimulation of lipolysis by isoproterenol. The results demonstrate that a combina tion of caloric restriction and STH was effective in normalizing body weight and composition of gain in the obese Zucker rat.