3,5-Dimethyl-3'-isopropyl-L-thyronine (DIMIT) and 
3,5-diiodo-3'-isopropylthyroacetic acid (IpTA2), two thyroid hormone analogs, 
have been tested in genetically obese Zucker rats and their lean littermates, in 
comparison with thyroxine (T4) and triiodothyronine (T3) for their thyromimetic 
activities on body weight gain and lipid levels in serum and liver. The 
compounds were administered for 9 weeks by orogastric tube to 6- to 8-week-old 
animals. While body weight gain remained practically unchanged in the lean rats, 
it decreased significantly in the obese individuals, especially with IpTA2. The 
serum lipid concentrations were also decreased in the obese rats in comparison 
with their lean littermates, especially with DIMIT. The connection observed 
between the structure of DIMIT and IpTA2 on one hand and their effects on the 
other is in good agreement with previous studies. Our results confirm that the 
iodine substituents are not necessary for thyromimetic activity and demonstrate 
that the isopropyl substituent in 3' plays an important role in the serum 
lipid-lowering effect of the thyroid hormone analogs tested.