Ione A. Kourides

THYROID HORMONE, OESTROGEN, AND GLUCOCORTICOID EFFECTS ON TWO DIFFERENT PITUITARY GLYCOPROTEIN HORMONE ALPHA SUBUNIT POOLS

Seven hypothyroid women (six postmenopausal and one premenopausal) were treated with 200 or 300 μg of levo‐T4 daily in order to suppress the secretion of TSH and its alpha and beta subunits. After such therapy, serum TSH and beta subunit of TSH (TSH‐β) levels were usually not detectable. Serum alpha decreased from a mean value of 4.5 ± 0.8 ng/ml to 2.8 ± 0.4 ng/ml (P > 0.01). Serum LH and FSH levels were unchanged. Oestrogen administration (20 mg diethylstilboestrol daily for 3 or 5 days) to these patients further decreased mean serum alpha to 1.9 ± 0.2 ng/ml (P > 0.005). In addition serum LH, FSH, and the beta subunits of LH and FSH decreased with oestrogen treatment. In separate experiments glucocorticoids (dexamethasone 4 mg every 6 hours for 10 doses) were administered to eight normal individuals, four women with decreased thyroid reserve, and one hyper‐thyroid woman. Not only did basal and TRH‐stimulated TSH secretion decrease, but secretion of alpha and TSH‐β also decreased after dexamethasone administration, with the largest fall in the patients with decreased thyroid reserve. The change in these thirteen patients’ alpha subunit increment after TRH administration was from a mean of 1.6 to 1.0 ng/ml with glucocorticoids; the change in TSH‐β was from a mean of 1.1 to 0.7 ng/ml. Serum LH and FSH concentrations were not altered by glucocorticoid administration. These studies have demonstrated two different pools of alpha subunits in the pituitary gland. Thyroid hormone and glucocorticoids decreased secretion of alpha subunits arising from the thyrotroph; oestrogen decreased secretion of alpha subunits arising from the gonadotroph.