Thyrotropin in human breast milk.

The thyrotropin (TSH) content of human breast milk was investigated, using both direct 125I-TSH radioimmunoassay and radioimmunoassay preceded by a partial purification step of elution from concanavalin A-Sepharose 4B. 15 samples of human milk between 1 and 13 weeks post-partum were found to contain 2.0 +/- (SD) 0.9 microU TSH/ml when assayed after Con A-extraction and adjusted for recovery by interpolation of a standard curve of Con A-extracted TSH standards. Recovery of 125I-hTSH tracer from both serum standards (58.6 +/- 5.5%; n = 10) and milk (53.6 +/- 6.7%; n = 15) were comparable. TSH levels obtained post-extraction were not significantly different from those that TSH is present in human breast milk in low concentrations, comparable to those normally found in the serum of euthyroid adults.