A sensitive and practical bioassay for thyrotropin using cultured FRTL-5 cells: assessment of bioactivity for serum TSH in patients with chronic renal failure

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Abstract
A sensitive bioassay for TSH employing a practical extraction method was developed, and the bioactivities in patients with chronic renal failure receiving hemodialysis were compared with those in normal subjects. Serum samples were obtained from 12 normal subjects and 12 patients with chronic renal failure receiving hemodialysis. TSH was extracted from the serum using anti-human TSH monoclonal antibody coated tubes, followed by elution with 2.0 mol/l guanidine-HCl solution (pH 3.2). After the eluate had been dialyzed against phosphate buffered saline (pH 7.4) and again against Tris-HCl solution (pH 7.4) and then lyophilized, it was reconstituted with hypotonic Hanks'' solution. Bioassay for TSH was performed by measuring the levels of cAMP released into the medium from cultured FRTL-5 cells incubated with the extract. The mean immunoreactive recovery rates of TSH from the serum in normal subjects and patients with chronic renal failure were about 42% (.+-. 6) and 40% (.+-. 2), respectively. The present bioassay was sufficiently sensitive to detect a serum TSH level of 1.0 mU/l when 3.0 ml of serum was used. Extracts from standard sera at concentrations ranging from 1.0 to 10 mU/l added to the culture medium caused significant linear increases in cAMP production. Based on analysis of covariance the regression line between the immunoreactivities and bioactivities of serum TSH in patients with chronic renal failure (y = 0.90x + 0.3, r = 0.92) was not significantly different from that in normal subjects (y = 1.04x + 0.1, r = 0.93). These results suggest that the present bioassay for TSH is sensitive and practical, and that the bioactivity of TSH in patients with chronic renal failure is similar to that in normal subjects.