Luteinizing Hormone (LH) Secretory Burst Duration Is Independent from LH, Prolactin, or Gonadal Steroid Plasma Levels in Amenorrheic Women

Abstract

The possible presence of LH pulsatile secretion has been studied in patients with hypothalamic amenorrhea [LH plasma levels, less than 3 (n = 35) or greater than 3 IU/L (n = 18)], amenorrhea associated with hyperandrogenemia (n = 31), or hyperprolactinemia (n = 10). Patients were sampled every 10 min for 4 h, and LH plasma concentrations were determined by the use of an immunofluorimetric assay. The program Detect was used for both pulse detection and data deconvolution, i.e. for instantaneous secretory rate computation, on LH time series. The presence of episodic LH secretion was observed in all patients, and LH pulse frequency ranged between 3.5 +/- 0.3 and 3.8 +/- 0.2 peaks/4 h among the four groups. LH pulse amplitude was significantly reduced in patients affected by hypothalamic amenorrhea with LH plasma levels lower than 3 IU/L (0.7 +/- 0.1 IU/L; P less than 0.01) and significantly increased in patients with hyperandrogenic amenorrhea (6.8 +/- 0.3 IU/L; P less than 0.01) compared to levels in the other groups under study. Instantaneous secretory rate computation permitted the optimal resolution of the secretory events and demonstrated that the duration of gonadotrope secretory bursts ranged from 22.8 +/- 1.4 to 26.8 +/- 2.3 min in amenorrheic patients and did not depend on LH, PRL, or sex steroid plasma levels. In conclusion, the present study shows the presence of significant LH pulsatile release in amenorrheic patients, suggesting that in amenorrheic, as in normally cycling, women the secretory bursts from the gonadotropes have the same duration, despite the plasma LH, PRL, or steroid hormone levels.