Abstract
The effects of thyroxine and its related derivatives on γ-aminobutyric acid (GABA) receptors in the rat brain were examined. d-Thyroxine strongly inhibited [ 3H]flunitrazepam binding to benzodiazepine receptor in crude synaptic membrane from the rat brain. The Scatchard analysis of the [ 3H]flunitrazepam binding in the presence of d-thyroxine indicated the decreases in the affinity and maximum number of binding site. Furthermore, d-thyroxine inhibited the enhancing effect of flunitrazepam on GABA-stimulated 36Cl − influx into membrane vesicles, although GABA-stimulated 36Cl − influx alone was not affected by d-thyroxine. On the other hand, the effects of thyroxine and its related derivatives on cerebral GABA B receptor binding were not noted. These results suggest that d-thyroxine may be a drug which is able to modulate the function of GABA A receptor complex via the inhibitory action on benzodiazepine recognition site.
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