Abstract
Plasma LH and FSH responses to the intravenous injection of synthetic LH-RH were studied in 18 normal males and in 24 patients with hypogonadism of various etiologies. Intravenous injection of 100, 200 and 400μg of LH-RH into normal adult males caused a dose-dependent rise in plasma LH and FSH. Plasma LH rose significantly in all subjects after 100μg of LH-RH, whereas 200 ti 400μg were necessary to achieve a consistent rise in plasma FSH.
In 7 patients with hypergonadotropic hypogonadism, plasma LH and FSH levels were elevated with a marked and sustained response to 100μg of LH-RH.
In 9 patients with isolated gonadotropin deficiency, plasma LH and FSH levels were either undetectable or low and their responses to 100μg of LH-RH were absent or limited.
In 5 of these patients, intravenous infusion of 400μg of LH-RH for 7 to 21 successive days improved plasma LH and FSH responsiveness to LH-RH, whereas the infusion for 2 days in 2 patients was not effective.
In 8 patients with failure of sexual maturation due to organic hypothalamohypophyseal lesions, plasma LH and FSH responses to 100μg of LH-RH were normal in one and low or absent in the remaining patients. In one patient with ectopic pinealoma, a diminished response of LH and FSH to LH-RH was normalized after 7 successive days treatment with the intravenous infusion of 400μg of LH-RH.
Synthetic LH-RH test is a useful tool for the differential diagnosis of hypogonadism. It is not always possible, however, to differentiate the hypothalamic from pituitary lesions by a single LH-RH test, because diminished response to LH-RH may indicate either pituitary lesions or pituitary hyporesponsiveness due to long-standing deficiency of endogenous LH-RH. In this regard, prolonged LH-RH stimulation test may help to differentiate between hypothalamic and pituitary lesions.
