IMPAIRED SENSITIVITY OF THE HYPOTHALAMO-PITUITARY-THYROID AXIS TO THE SUPPRESSANT EFFECT OF DEXAMETHASONE IN ELDERLY SUBJECTS

It has been shown that glucocorticoids have a suppressant effect on the thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH) in young men. To assess whether this effect of corticosteroids is also present in aged individuals, six young subjects (aged 26-32 years) and six elderly men (aged 68-75 years) underwent, in random order, at 1 week intervals, three TRH stimulation tests 30 min after IV administration of placebo and 2 mg and 4 mg dexamethasone phosphate. Elderly men showed higher basal plasma levels of TSH (P < 0.02) and lower plasma levels of FT3 (P < 0.03) and FT4 (P < 0.01). The TSH response to TRH was significantly lower in aged subjects than in young ones (P < 0.009). Moreover, 2 mg dexamethasone significantly blunted the TSH response to TRH in young men (P < 0.0001), but not in the elders. The inhibitory effect of the glucocorticoid on the TRH-induced TSH secretion, in aged subjects, was evident only after 4 mg dexamethasone administration (P < 0.0001). These data confirm that glucocorticoids have an inhibitory role on the thyrotropic axis and show, for the first time, that normal elderly men are hyporesponsive to this suppressant effect of corticosteroids.