Pulsatile Secretion of Immunoreactive a-Subunit in Man*

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Abstract
We compared the secretion of uncombined ±-subunit with LH secretion, as measured by RIA in six normal men, an agonadal adult man, and an adult woman with testicular feminization. Blood samples were drawn every 10 min for 12 h t o evaluate pulsatile LH and free ± secretion. Spontaneous a pulses occurred every 120 ± 60 min (mean ± SD; range, 40-260) i n eugonadal men. The mean a pulse amplitude was 0.49 ± 0.11 ng⁄ml, representing an increase of 60 ± 18% above the preceding nadir value, ± pulses were generally associated with LH pulses, and the amplitudes of concordant ± and LH pulses were highly positively correlated (r = 0.58; P< 0.01). The absolute amplitude of concordant ± peaks was 1.5 ± 0.7% that of corresponding LH peaks. Additional ± pulses were noted in each subject for which simultaneous LH fluctuations failed to meet the criteria for pulses. Studies in the agonadal man and in the patient with testicular feminization revealed that the frequency of both spon-taneous a and LH pulses was increased to approximately twice that in normal men. Gel filtration analysis indicated that all ± radioimmunoactivity in normal male sera coeluted with [l25I]±. By contrast, in hypogonadal sera, only 50-60%of a immuno-reactivity coeluted with [125I]±, the remaining activity appeared i n the region of LH and FSH and resulted from RIA cross-reactivity. We conclude that uncombined ±-subunit, as well as LH is normally released into the peripheral blood in discrete pulses. In the absence of exposure to androgen, the frequency of these pulses increases, presumably as a consequence of the accelerated release of LRH. However, ± RIAs overestimate the concentration of uncombined oc in hypogonadal sera. We propose that the coanalysis of LH and ± secretory episodes may prove useful in resolving some of the complexities associated with gonadotropin secretory patterns.