Although
TRIAC is bound at least twice as avidly to
nuclear receptor as T3, its thyromimetic potency is relatively low and its effect at the pituitary level on
thyrotropin (TSH) secretion seems to be dissociated from that at the peripheral tissue level. In order to gain further insight into the complex effects of this
thyroid hormone analog, we studied the effects of long-term
TRIAC administration (2.8 mg/day for 2 months) on TSH secretion, circulating free
thyroid hormone (FT4 and FT3) levels and some parameters able to evaluate the peripheral
thyroid hormone action, in 5 mild obese subjects on low caloric diet (1200 kcal/day). The results were compared to those obtained in 5 mild obese subjects matched for age, sex and weight on low caloric diet alone.
TRIAC administration completely inhibited the secretion of both basal and TRH-stimulated TSH in few days, and consequently serum FT4 and FT3 concentrations progressively dropped to very low levels, while no significant changes in both TSH and free
thyroid hormone levels were recorded in the control group. The
body weight significantly fell in both groups, without any difference between
TRIAC treated and untreated patients. The heart rate was constant throughout the course of the study in both groups of patients. Serum total
cholesterol,
triglyceride and total
lipid concentrations significantly decreased in both groups, and the decrement recorded in
TRIAC treated patients was not significantly different from that found in patients on diet alone.(ABSTRACT TRUNCATED AT 250 WORDS)