Antidepressant-like effects of triiodothyroacetic acid in mice

Triiodothyroacetic acid in health and disease

Thyroid hormone (TH) is crucial for development and metabolism of many tissues. The physiological relevance and therapeutic potential of TH analogs have gained attention in the field for many years. In particular, the relevance and use of 3,3',5-triiodothyroacetic acid (Triac, TA₃) has been explored over the last decades. Although TA₃ closely resembles the bioactive hormone T₃, differences in transmembrane transport and receptor isoform-specific transcriptional activation potency exist. For these reasons, the application of TA₃ as a treatment for resistance to TH (RTH) syndromes, especially MCT8 deficiency, is topic of ongoing research. This review is a summary of all currently available literature about the formation, metabolism, action and therapeutic applications of TA₃.

Triiodothyronine (T3) modifies cholinergic-induced hypothermia and tremor in rats

Hypothermia and tremor responses of oxotremorine and eserine were studied in rats after several T3 treatment regimens. The T3 antagonized oxotremorine-induced hypothermia and failed to antagonize eserine hypothermic effect, but potentiated oxotremorine- and eserine-induced tremors. Acetylcholinesterase activity was not altered in T3 rats. The hypothetical mechanisms to explain changes of central cholinergic responses caused by T3 are discussed.

Gonadotropin-releasing hormone (GnRH) as antidepressant: a psychopharmacological animal study

Because the secretion of gonadotrophic hormones is disturbed in some depressive states, it has been hypothesized that gonadotropin-releasing hormone (GnRH) has antidepressant properties in humans, but no clear information has emerged from clinical trials. The lack of experimental psychopharmacological data prompted us to investigate the effects of GnRH on the 'learned helplessness' behavioral model of depression in rats. GnRH was injected i.p. at doses of 0.06, 0.25, 0.50, 1 and 2 mg/kg per day. GnRH significantly reduced the number of escape failures at doses of 1 mg/kg per day or higher during the first shuttle-box session and at doses of 0.25 mg/kg per day onwards during the third shuttle-box session. These antidepressant-like effects of GnRH were similar to those observed with the tricyclic antidepressants imipramine (32 mg/kg per day) or clomipramine (32 mg/kg per day) in the same model. Moreover, while the induction of learned helplessness behaviour resulted in a fall in the plasma levels of FSH and LH, normal values of these hormones could be restored by a behaviorally effective GnRH regimen. From these data it can be suggested that GnRH exhibits an interesting antidepressant-like activity in rats.

Triiodothyroacetic acid (TRIAC) potentiation of antidepressant-induced reversal of learned helplessness in rats

The results of several clinical investigations have suggested that a special relationship exists between thyroid function and affective disorders and/or the therapeutic response to antidepressants. Animal studies have shown the possible beta-adrenergically mediated antidepressant-like properties of triiodothyroacetic acid (TRIAC) in rodents. The present experiment showed (1) that the reversal by antidepressants (clomipramine or imipramine) of escape deficits produced by previous exposure to uncontrollable shock was significantly hastened in animals given TRIAC and (2) that L-penbutolol treatment prevented the elimination of helpless behavior induced by TRIAC, suggesting a beta-adrenergic mediation of the antidepressant activity of thyroid compounds. The study confirmed that learned helplessness might be a useful model for studying in animals the neurohormonal correlates of affective disorders and the neurobiochemical basis of the enhancement of the antidepressant action produced by thyroid compounds.