SOME ASPECTS OF THYROID FUNCTION IN RATS AFTER FEEDING OF LEVOMEPROMAZINE

¹ Department of Pharmacology, University of Toronto, Toronto, Canada

Rats fed levomepromazine for varying periods of time showed a significant growth depression. Otherwise, treated rats looked healthy and were indistinguishable in appearance from their controls.

An analysis of variance of relative thyroid weights showed treated animals to have smaller thyroids than their respective controls. This depression of thyroid size increased with the duration of treatment.

The proportion of beta cells in pituitaries was decreased in animals treated for 14 and 42 days. The proportion of alpha cells in the glands was increased in treated rats.

Rats fed levomepromazine had a decreased content of radioactive iodine and/or hormones in their thyroids 24 hours following tracer administration. The analysis of variance of these data showed that the thyroid-depressing effect of the drug increased with the duration between tracer injection and sacrifice and that the drug influenced the I¹³¹ content of the gland by more than one mechanism.

Plasma as well as kidney radioactivity was significantly lower in treated than in control animals.

It was concluded that the decrease in radio-activity in thyroid glands of treated animals was due to a combination of accelerated excretion of iodide through the kidney and of decreased stimulation of the thyroid gland by the pituitary.