SECRETION OF ALPHA AND BETA SUBUNITS OF TSH BY THE ANTERIOR PITUITARY

We have attempted to determine whether blood concentrations of the α chains of TSH arise by direct pituitary secretion of α chain or by degratation of the intact hormone after secretion. Highly purified human TSH was administered by infusion to euthyroid volunteers; blood TSH concentrations were raised to 36 μu/ml. After TSH infusion, circulating blood α chain concentrations did not change. The same volunteers received an infusion of TRH which stimulated pituitary secretion of TSH, raising blood concentrations to 15 μ/ml in one series of subjects and to 23 μu/ml in a second series. After TRH, blood concentrations of α chain increased from undetectable to over 400 pg/ml. We conclude that α subunits of TSH are directly secreted by the pituitary gland and are not formed by degradation of intact TSH in the peripheral circulation.