Human prolactin and thyrotropin concentrations in the serums of normal and hypopituitary children before and after the administration of synthetic thyrotropin-releasing hormone

Synthetic thyrotropin-releasing hormone (TRH) was administered to normal children and hypopituitary patients in a dose of 7 μg/kg i.v. over 30-60 sec. Serum thyrotropin (TSH) and prolactin (HPr) concentrations were measured by radioimmunoassay before and at 15-min intervals for 2 hr after TRH. In 20 normal children HPr rose from a mean baseline value of 7.0±1.2 (SEM) ng/ml to a mean peak value of 39.5±5 ng/ml.

In 11 patients with growth hormone (GH) deficiency without TSH deficiency. HPr values rose from a mean baseline of 3.6±0.8 ng/ml to a mean peak value of 13.9±2.8, a significantly less peak response as compared with normal children (P < 0.005). The TSH responses to TRH, however, were statistically indistinguishable from those of normal children.

In 10 patients with GH and TSH deficiency both the mean baseline HPr levels (25.0±5 ng/ml) and the mean peak HPr levels after TRH (68.5±10 ng/ml) were significantly higher (P < 0.005 and < 0.025) than those of normal children. Similar comparisons were also true for the peak TSH responses (P < 0.05). Two panhypopituitary patients released no TSH and only small amounts of HPr after TRH. After thyroid replacement therapy in eight of the patients with GH and TSH deficiency, the mean HPr baseline levels (7.6±1.0 ng/ml) and peak levels (23.3±4.6 ng/ml) after the same dose of TRH were significantly less than their pretreatment levels (P < 0.001 and < 0.01) and were within the range for normal children.

Synthetic TRH stimulates the simultaneous release of TSH and HPr in normal children and most hypopituitary patients. When the concentrations of thyroxine (T4) and triiodothyronine (T3) are low, the levels of HPr before and after TRH are elevated. After thyroid replacement therapy, HPr levels decrease to normal. T4 and/or T3 may condition the production or effects of prolactin-inhibiting factor (PIF) activity. The TSH and HPr responses after TRH in hypopituitary patients will determine whether the primary defect resides in the pituitary or hypothalamus, but cannot delineate the hypothalamic defect as a deficiency of hypothalamic hormone production or neurohumoral transmission.

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