Secretion of Alpha and Beta Subunits of TSH by the Anterior Pituitary

Abstract

S U M M A R YWe have attempted to determine whether blood concentrations of the a chains of TSH arise by direct pituitary secretion of a chain or by degradation of the intact hormone after secretion. Highly purified human TSH was administered by infusion to euthyroid volunteers ; blood TSH concentrations were raised to 36 pu/ml. After TSH infusion, circulating blood c1 chain concentrations did not change. The same volunteers received an infusion of TRH which stimulatedpituitary secretion ofTSH, raising blood concentrations to 15 pu/ml in one series of subjects and to 23 pulml in a second series. After TRH, blood concentrations of a chain increased from undetectable to over 400 pg/ml. We conclude that a subunits of TSH are directly secreted by the pituitary gland and are not formed by degradation of intact TSH in the peripheral circulation. I N T R O D U C T I O NTSH is known to consist of two dissimilar peptide chains, u and fi (Cornell & Pierce, 1973;Pierce et al., 1971). The exact biomolecular mechanisms involved in synthesis and union of these two chains have not been elucidated. The presence of separate subunits in the peripheral circulation, however, has been observed in hypothyroidism before and after TRH (Kourides et al., 1973; Benveniste et al., 1973), but subunit measurement in normal humans after TRH have not yet been reported. In addition, the question of how these subunits appear in the peripheral circulation has not yet been resolved. Two possibilities exist: (1) the a or fi chains may be directly secreted by the pituitary, (2) the intact hormone may be secreted and the subunits then formed by degradation of the intact hormone in the peripheral tissues. To resolve these possibilities, we have infused intact, purified human TSH to normal volunteers and compared the results to those obtained after stimulation of pituitary

Serum glycoprotein hormone alpha subunit levels in patients with cancer

“…Elevated serum levels of the alpha subunit have been found in patients with primary myxedema associated with high circulating No. 5 levels of TSHI7 in some patients with pituitary adenomas" and in patients with renal fail-Enhanced secretion of the subunit by the pituitary may account for the elevated levels in hypothyroid patients and those with pituitary tumors, while reduced renal clearance or other metabolic abnormalities associated with uremia may elevate the blood alpha subunit concentration.…”

Thyroid Hormone, Oestrogen, and Glucocorticoid Effects on Two Different Pituitary Glycoprotein Hormone Alpha Subunit Pools

“…We and other investigators have reported that the normal pituitary gland contains a marked predominance of alpha subunits relative to the beta subunits of the pituitary glycoprotein hormones (Kourides et al, 1975;Prentice and Ryan, 1975;Hagen and McNeilly, 1975c;Kaplan et al, 1976;Vanhaelst and Golstein-Golaire, 1976). These subunits can be directly released from the pituitary in response to hypothalamic releasing hormones (Kourides et al, 1975;Edmonds et al, 1975a;Edmonds et al, 1975b;Kourides et al, 1977). The present study provides further evidence for separate alpha subunit pools, one arising from the thyrotroph and one from the gonadotroph.…”

“…Normal postmenopausal women have elevated serum alpha concentrations compared to premenopausal women and men (Kourides et al, 1975;Hagen & McNeilly, 1975a). Serum alpha levels demonstrate greater increases after LHRH than after TRH in normal individuals (Edmonds et al, 1975a;Edmonds et al, 1975b;Hagen & McNeilly, 1975b;Kourides et al, 1977). Although serum alpha demonstrates no increase after TRH in hyperthyroid patients, alpha increases appropriately after LHRH administration (Kourides et al, 1977).…”