Reproductive & gonadal
The pulsatile cascade that governs the reproductive axis.
GnRH · LH · FSH · kisspeptin · hCG
Overview
The hypothalamic–pituitary–gonadal (HPG) axis runs on rhythm. GnRH is released from the hypothalamus in pulses, driving the anterior pituitary to secrete the gonadotropins LH and FSH, which in turn act on the gonads to produce sex steroids and gametes.
Upstream of GnRH, kisspeptin is the key gatekeeper that gates pulse generation — a comparatively recent addition to the model of how the axis is switched on. hCG, structurally similar to LH, sustains the corpus luteum in early pregnancy.
The defining feature of this axis is pulse frequency: the same hormone, delivered in pulses versus continuously, produces opposite downstream effects — the basis for both stimulation and suppression strategies.
Key signals
Pulsatile hypothalamic driver of the gonadotropins.
Triggers ovulation and gonadal steroidogenesis.
Drives follicular development and spermatogenesis.
Upstream gatekeeper that gates GnRH pulse generation.
LH-like; sustains the corpus luteum in early pregnancy.
Reference notes
- Pulsatile GnRH stimulates the axis; continuous GnRH-agonist exposure paradoxically suppresses it via receptor desensitization.
- Kisspeptin reframed the model of how puberty and the reproductive axis are switched on.
- LH and hCG share receptor activity, which is why hCG can substitute for an LH signal in some contexts.
Analogs & therapeutics
Engineered molecules built on this family’s biology — same receptors, re-tuned for stability and duration.