Evaluation of the human gonadotroph free α-subunit secretory pools by administration of gonadotropin hormone-releasing hormone into normal subjects at different phases of the ovarian cycle

Abstract

The specificity of a monoclonal antibody RIA for the measurement of free alpha-subunit in plasma is presently documented. This RIA was used to explore the pituitary gonadotroph free alpha-subunit reserve in normal ovulating women stimulated with gonadotropin hormone-releasing hormone (GnRH). RIA specificity was established by means of competitive inhibition curves with various glycoprotein hormone preparations, and Sephadex G-100 exclusion chromatography of purified hFSH (1-2), hLH (LER 960) and pituitary extract. The 3.8% and 5.5% crossreactivities of hFSH 1-2 and hLH LER 960 were shown by exclusion chromatography to result in part from free alpha-subunit contamination in these purified preparations. Pituitary extract chromatography indicated hFSH and hLH cross-reactivity below 2.5% and 1.5%, respectively. Normal females were stimulated with GnRH throughout the cycle: 3 tests were performed on Day 7, 1 test on Day 13, 16, 17 and 22, respectively, and 2 tests on Day 24. GnRH stimulation consisted of an initial 100 micrograms bolus (time 0) followed at 2 h by a 12.5 micrograms/h constant infusion, and a second 100 micrograms bolus at 5 h. In all subjects, baseline free alpha-subunit values were below 2 ng/ml. Total free alpha-subunit secretion was markedly enhanced in subjects Day 13 and 16, in concert with total hLH and hFSH secretion. In the three subjects Day 7, free alpha-subunit was released only after the second GnRH bolus. In periovulatory subjects, free alpha-subunit secretion became apparent after the initial bolus and with constant GnRH infusion. In the three subjects Day 22 and 24, peak levels of free alpha-subunit were obtained after the second GnRH bolus.(ABSTRACT TRUNCATED AT 250 WORDS)