Impaired Prolactin Response to Thyrotropin-Releasing Hormone in Isolated Gonadotropin Deficiency and Exaggerated Response in Primary Testicular Failure*

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Abstract
Six males with isolated gonadotropin deficiency (group I) and 6 with primary testicular failure (group II) received LRH (100 μg) and TRH (200 μg) 30 min later. Their responseswere compared to 15 male controls. In group I, basal LH, FSH, testosterone, and estradiol values were all less than the controls (P < 0.001). In group II, basal gonadotropins were elevated (LH, P < 0.05; FSH, P < 0.001), although testosterone and estradiol values were similar to the controls. The peak gonadotropin responses to LRH were impaired in group I (P < 0.001) and exaggerated in group II (P < 0.001). Mean (±SEM) basal PRL levels in group I were 7.2 ± 0.5 vs. 11.0 ± 1.0 ng/ml in the controls (P < 0.01). Levels in group II were 14.3 ± 1.6 ng/ml and were not significantly different from controls. The mean peakPRL response to TRH in controls was35.8 ± 3.9 ng/ml. In group I, the peak was 13.4 ± 1.5 ng/ml (P < 0.001), and it was 77.4 ± 9.0 ng/ml in group II {P < 0.001). Long term treatment with hCG in three subjects of group I and testosterone enanthate in one additional subject was associated with a rise in basal testosterone, estradiol, and PRL levels and restoration of PRL response to TRH. Cessation of hCG treatment in two of these subjects was accompanied by a return to the pretreatment state. These results suggest that the impaired PRL response in isolated gonadotropin deficiency may not be an integral component of thesyndrome but, rather, a consequence of the altered steroid milieu. A direct correlation existed between the estradiol to testosterone ratio and the peak PRL response to TRH in group II and the controls. In the same two groups, an inverse correlation also existed between basal testosterone and peak PRL response to TRH. This suggests that the exaggerated PRL response in primary testicular failure may be related to a relative increase in estradiol or reduction in testosterone.