Alterations of the hypothalamic GnRH interpulse interval sequence over the normal menstrual cycle.

Luteinizing hormone (LH) is released in a pulsatile fashion from the anterior pituitary in response to hypothalamic gonadotropin-releasing hormone (GnRH) secretion. Previous autocorrelation analysis of the sequence of interpulse intervals of LH secretion in normal men has supported the hypothesis that the underlying hypothalamic mechanism of GnRH secretion governing episodic LH release is a renewal process, indicating that hypothalamic "memory," if present, does not extend back further in time than the preceding secretory pulse. A similar analysis of pulsatile LH secretion was undertaken in 45 studies of normal women, obtained throughout the menstrual cycle. Analysis of these studies revealed a process consistent with renewal throughout the follicular and early luteal phases. However, this relationship appears to break down in the mid-to-late luteal phase, indicating that alternative feedback pathways provide an overriding influence on the underlying renewal process of hypothalamic GnRH secretion. Pulsatile progesterone secretion by the corpus luteum, which first emerges at this stage of the menstrual cycle, may be the agent responsible for this feedback.

Interpulse interval sequence of LH in normal men essentially constitutes a renewal process.

Luteinizing hormone (LH) is released from the anterior pituitary gland in an episodic pattern driven by pulses of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Autocorrelation analysis of the sequence of interpulse intervals of LH secretion in normal men supports the hypothesis that the underlying mechanism driving LH secretion is a renewal process. That is, whatever "memory" the GnRH pulse generator (i.e., the hypothalamus or its antecedent neural drive) may have, it does not go back in time further than the preceding secretory pulse. Thus the hypothalamic timer starts over again each time there is a GnRH secretory episode.