Effects of i.v. TRH on LH, FSH and GH serum levels in primary hypothyroid children

Abstract

The occurrence of precocious puberty in children with primary hypothyroidism is a well recognized but poorly understood phenomenon. Several mechanisms have been proposed, but exceptions can be raised for each hypothesis (Lindsay et al, Am J Dis Child 134, 588, 1980). In 9/12 off-therapy primary hypothyroid children and adolescents (aged 1-16 yrs, 9 prepubertal and 3 pubertal) i.v. TRH (5μg/kg) injection elicited an evident increase of serum LH between 15 and 30 min, which exhausted within 90 min. Mean (± SEM) LH serum levels at 15 (2.22±0.45 ng/ml) and 30 min (2.22±0.43) were significantly (p 7 ng/ml)was also recorded in 3/12 hypothyroids. On the contrary FSH serum levels were not substantially modified by TRH bolus, either in the patient or in the control group. An overlap in the pituitary hormonal feed-back mechanism had been hypothesized to explain the occurrence of precocious puberty in primary thyroid failure (Van Wyk and Grumbach, J Pediatr 57, 416, 1960). The nonspecific LH-releasing effect of TRH in our patients especially evident in the pubertal ones supports such hypothesis.