Effect of a single dose of glucocorticoid on the diurnal variations of TSH, thyroxine, 3,5,3'-triiodothyronine, 3,3',5'-triiodothyronine and cortisol in normal men.

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Abstract
Plasma thyrotropin (TSH) and cortisol concentrations were suppressed immediatelyafter an intravenous bolus dose of8mg betamethasone in 6 male subjects. The circadian variations of these hormones disappeared for40hr (TSH) and44hr (cortisol). Plasma thyroxine (T4), 3, 5, 3'-triiodothyronine (T3), 3, 3', 5'-triiodothyronine (reverse T3) levels did not show diurnal variations before betamethasone administration. Plasma T3levels decreased to 66% of the basal levels 20hr after batamethasone administration, whereas plasma reverse T3levels increased to163% of the basal levels at 24hr. These changes were reversed by3to5days after betamethasone. Theearlier recovery of the diurnal rhythm of TSH than that of cortisolsuggests thatthe TSH rhythm is not under the direct control of circulating cortisol.