Comparative study of imipramine, amitriptyline and their desmethyl analogues in the hypothyroid rat

The effects of thyroid state on beta-adrenergic and serotonergic receptors in rat brain

The effects of hyperthyroidism or hypothyroidism, alone or in combination with the tricyclic antidepressant desmethylimipramine (DMI), on brain beta-adrenergic and serotonin (5HT2) receptors were studied in adult male Sprague-Dawley rats. Intraperitoneal administration of T3 or T4 for 7 days increased the number of cortical beta-adrenergic and 5HT2 receptors. These increases were significant at levels of 250 micrograms/kg or above for both hormones. Neither thyroidectomy nor "reverse" T3 (rT3) (500 micrograms/kg) produced an effect on either receptor type. The down-regulation of beta-adrenergic receptors produced by daily subcutaneous injections of 20 mg/kg of DMI for 7 days was partially offset by concurrent administration of T4, whereas the down-regulation of 5HT2 receptors produced by the drug was not affected by concurrent administration of either T3 or T4. Hypothyroidism (thyroidectomy) did not significantly affect the adaptation of these receptor populations to DMI. As regards brain regions other than cortex, T4 (250 micrograms/kg) produced the same changes in hippocampus as in cortex, while thyroidectomy decreased beta-adrenergic receptors only in the cerebellum. Thyroxine also elevated 5HT2 receptors in the hippocampus; thyroidectomy caused a significant decrease in 5HT2 receptors in the striatum.

Thyroid hormones in the treatment of affective disorders

The experience of using thyroid hormones in affective disorders is summarized. This includes: 1) Using thyroid hormones alone in depression; 2) their combined use with tricyclic antidepressants; 3) addition of thyroid hormones to nontricyclic antidepressants; 4) the use of thyroid stimulating hormone; and 5) thyrotropin releasing hormone in depression. Suggested mechanisms of action are discussed. A special attention is paid to the place of thyroid hormones in the treatment of rapid cycling affective disorder.