LRH-stimulated release of bioactive and immunoreactive LH in a patient with the XX male syndrome.

Serum levels of biologically active LH (bLH) and immunoreactive LH (iLH) under basal conditions and in response to the iv injection of 0.1 mg synthetic LRH were measured in a 15-year-old boy with the 46,XX karyotype. LH bioactivity was assessed "in vitro" on mouse Leydig cell preparations, whereas iLH levels were measured by a double antibody RIA technique. High basal levels of both bLH and iLH were shown in the XX male. Following LRH administration, the relative maximum response of LH above basal levels (LH delta %) was higher for iLH than for bLH. Consequently, the LH bioactivity to immunoreactivity (b/i) ratio decreased from basal values. Since a similar decrease in the b/i ratio of LRH-stimulated LH has been observed in patients with Klinefelter's and Turner's syndrome, we can suppose that in the chromosomal disorders of sex differentiation the pituitary gland possesses a lower responsiveness for bLH than the normal pituitary.