3,5,3'-triiodothyroacetic acid (
TRIAC) has been used to suppress pituitary TSH secretion with reported attenuation of extrapituitary effects. We investigated whether equivalent doses of T (3) and
TRIAC preventing the induction of
goiter by
methimazole (MMI) had a different or similar impact on peripheral tissues, such as liver and bone. In particular, we compared the effects of both compounds on the activity of the hepatic
thyroid hormone-responsive
enzymes, malic
enzyme and L-glicerol-3-P
dehydrogenase; bone mineral density and biochemical parameters of bone turnover, such as bone
alkaline phosphatase (b-ALP) and the carboxy-terminal telopeptide region of
type I collagen (beta-CTX); and the activity of thyroid
ornithine decarboxylase (ODC). We also compared the effects of T (3) and
TRIAC on the involution of MMI-induced
goiter. Our results showed that
TRIAC was more effective than T (3) to reduce MMI-induced
goiter in a short-term
goiter involution assay.
TRIAC increased hepatic
enzymes activity and beta-CTX levels, a parameter of
bone resorption, more than T (3). However, bone mineral density was not altered by either treatment. Both compounds even reduced ODC activity at doses that were not effective at the pituitary level. These results demonstrate increased
TRIAC hepatic and antigoitrogenic activity compared to T (3).
TRIAC induces an imbalance in bone remodeling without affecting bone mineral density. Further studies are required to clarify this point.