VARIABLE CARBOHYDRATE STRUCTURES OF CIRCULATING THYROTROPIN AS STUDIED BY LECTIN AFFINITY-CHROMATOGRAPHY IN DIFFERENT CLINICAL CONDITIONS

Carbohydrate structures of intrapituitary and circulating were studied by Concanavalin-A (Con A) and ricin lectin chromatography under diffe rent clinical conditions. Con A permits the separation of molecules di ffering in the extent of their carbohydrate branching, whereas ricin g ives an estimation of the degree of their sialylation. Intrapituitary TSH was more retained on Con A and less sialylated than circulating ho rmone, suggesting that carbohydrate chains of intrapituitary molecules are less mature than those present in the circulation. A greater prop ortion of TSH firmly bound to Con A, compared to control values, was f ound in sera from fetuses and patients with uremia, TSH-secreting aden omas, and central hypothyroidism. In primary hypothyroid patients, TSH binding to Con A was similar to that found in controls, but a greater percentage of sialylated forms was seen. In central hypothyroidism pa tients, TSH released in response to TRH was less sialylated. Interesti ngly, no sialylated TSH was found in normal fetuses. In conclusion, th e present data show that both TSH carbohydrate branching and sialylati on may vary in different clinical conditions. As some of the above cli nical conditions are known to be accompanied by variations in the bioa ctivity of circulating TSH, the finding of changes in TSH carbohydrate structures further supports the view that glycosylation modulates the expression of TSH biological activity.