Thyrotropin: α- and β-subunits of thyrotropin, and prolactin responses to four-hour constant infusions of thyrotropin-releasing hormone in normal subjects and patients with pituitary-thyroid disorders

TRH was administered as a 4-h constant rate iv infusion (0.4 µg/min) to eight healthy euthyroid volunteers, three euthyroidfemales on estrogen, eight hyperthyroid patients, eight patients with primary hypothyroidism, and five patients with hypothalamic and pituitary disorders. Blood was collected at regular intervals for the measurements of TSH, α and β-TSH subunits, T3 and PRL. Healthy euthyroid subjects exhibited biphasic increases in intact TSH as well as in α- and β-TSH subunits. Circulating TSH levels rose rapidly within 10 min of infusion to a peak in 45 min. Levels were then stable or decreasing until 90 min, when a second phase of increase occurred which was maximal at160 min. Greater responses were observed in females than in males. Primary hypothyroid patients exhibited similar biphasic increases in TSH and itssubunits as did euthyroid subjects. Patients with hypothalamic and pituitary disorders had delayed and diminished responses, while thyrotoxic patientsdid not respond at all. In euthyroid s...