The effects of desipramine (DMI) and electroconvulsive shock (ECS) on the function of the hypothalamo-pituitary-thyroid axis in the rat.

Monoaminergic systems influence the hypothalamo-pituitary-thyroid (HPT) axis. Since two different antidepressant treatments, desipramine (DMI) and electroconvulsive shock (ECS), are known to alter monoaminergic function in the rat central nervous system (CNS), the effects of DMI and ECS on the function of the HPT axis in the rat were examined. Animals were treated with either DMI (5 mg/kg) twice daily for 14 days (DMI x 14) or once only (DMI x 1) or ECS five times in 10 days (ECS x 5) or once only (ECS x 1). Three and 24 hours after the final treatment, blood samples were taken for measurement of plasma total thyroxine (TT4), total tri-iodothyronine (TT3), free thyroxine (FT4), free tri-iodothyronine (FT3) and thyroid stimulating hormone (TSH). Plasma TSH concentrations were decreased by the DMI x 14 and increased by the ECS x 5 regimen. Small decreases in thyroid hormones (T3 and T4) occurred after DMI x 14. No other consistent changes were observed in the animals treated with ECS. The effect of DMI or ECS treatment on the responsiveness of pituitary thyrotrophs was assessed in vitro. Isolated superfused pituitary glands from rats treated in vivo with either DMI x 14 or ECS x 5 were exposed to a pulse of thyrotropin releasing hormone (TRH; 1 ng/ml). No significant change in TSH secretion was observed in response to TRH in either case. Therefore, the changes observed in circulating plasma TSH levels are unlikely to have resulted from either direct or indirect effects on pituitary thyrotroph TRH receptor sensitivity.