Pulsatile secretion of immunoreactive alpha-subunit in man

Abstract

We compared the secretion of uncombined alpha-subunit with LH secretion, as measured by RIA in six normal men, an agonadal adult man, and an adult woman with testicular ferminization. Blood samples were drawn every 10 min for 12 h to evaluate pulsatile LH and free alpha secretion. Spontaneous alpha pulses occurred every 120 +/- 60 min (mean +/- SD; range, 40-260) in eugonadal men. The mean alpha pulse amplitude was 0.49 +/- 0.11 ng/ml, representing an increase of 60 +/- 18% above the preceding nadir value. alpha pulses were generally associated with LH pulses, and the amplitudes of concordant alpha and LH pulses were highly positively correlated (r = 0.58; P less than 0.01). The absolute amplitude of concordant alpha peaks was 1.5 +/- 0.7% that of corresponding LH peaks. Additional alpha 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 spontaneous alpha and LH pulses was increased to approximately twice that in normal men. Gel filtration analysis indicated that all alpha radioimmunoactivity in normal male sera coeluted with [125I]alpha. By contrast, in hypogonadal sera, only 50-60% of alpha immunoreactivity coeluted with [125I]alpha, the remaining activity appeared in the region of LH and FSH and resulted from RIA cross-reactivity. We conclude that uncombined alpha-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, alpha RIAs overestimate the concentration of uncombined alpha in hypogonadal sera. We propose that the coanalysis of LH and alpha secretory episodes may prove useful in resolving some of the complexities associated with gonadotropin secretory patterns.