THE EFFECTS OF MORPHINE, CHLORPROMAZINE AND RESERPINE ON PITUITARY-THYROID ACTIVITY IN RATS

¹ Department of Pharmacology, The Center for the Health Sciences and Brain Research Institute, University of California, Los Angeles, California

Studies were initiated to investigate the effects of some CNS depressants on pituitary-thyroid activity in rats. Daily administration of morphine (5-15 mg/kg) and chlorpromazine (5 mg/kg) inhibited the release of I¹³¹-labeled thyriod hormone, but reserpine, even in near lethal doses (0.25 and 2.5 mg/kg) bad no effect. Morphine and chlorpromazine as well as some stressful stimuli are known to increase the secretion of adrenal corticosteroids. Since administration of adrenal Corticosteroids has been shown to inhibit TSH secretion in rats and rabbits, the effects of morphine and chlorpromazine were further studied in adrenalectomize rats. These animals also showed inhibition of I¹³¹-labeled thyroid hormone release. Administration of TSH resulted in an increase in thyroid hormone output of animals pretreated with morphine or chlorpromazine. These data suggest that reduction in the TSH secretory rate produced by morphine and chlorpromazine promazine is mediated via interference with the central pathways concerned in the regulation of TSH release.

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