EFFECT OF FERROUS SULFATE ON THYROXINE REPLACEMENT THERAPY IN HYPOTHYROID RATS

The effect of simultaneous administration of ferrous sulfate on thyrox ine (T-4) therapy in hypothyroid rats was studied. 36 male rats were r endered hypothyroid by administration of (NaI)-I-131 and divided into three groups. Rats from Group 1 received oral doses of only T-4, Group 2 were given T-4 and ferrous sulfate simultaneously while Group 3 ani mals were given T-4 and ferrous sulfate with an interval of 4 h for 12 weeks. T-4, triiodothyronine (T-3), free T-4 (FT4), free T-3 (FT3) an d thyrotropin (TSH) levels were measured in the serum of all the rats initially in euthyroid state, when they were hypothyroid and 12 weeks after T-4 replacement therapy. After T-4 therapy, the mean serum T-4 l evel in Group 2 animals declined significantly in comparison to the in itial level from 8.1 +/- 1.4 mu g dL(-1) to 6.5 +/- 1.1 mu g dL(-1), ( p = 0.006). Group 2 rats also showed significant increases in their TS H levels from 1.62 +/- 1.32 ng mL(-1) to 5.76 +/- 3.58 ng mL(-1), (p = 0.009). Similarly the FT4 concentration fell significantly in Group 2 (p = 0.01). The differences in the initial (zero week) and final (12 weeks after T-4 therapy) levels in the three groups were also compared . In Group 2 animals, the change in final from initial mean TSH level showed significant increase as compared with difference found in Group 1 and Group 3. Similarly, FT4 levels showed significant decrease in t heir final from initial level as compared to the difference found in G roup 3. Simultaneous administration of ferrous sulfate and T-4 caused significant reductions in T-4 and FT4 and an increase in TSH levels. T hese effects were diminished when there was a sufficient gap between t he administration of the two drugs.