During the preovulatory LH surge, which shift in gonadotroph physiology allows GnRH to STIMULATE rather than desensitise LH release?

• A Progesterone priming converts GnRH receptor coupling from Gs to Gq
• B Oestradiol upregulates GnRH receptors on gonadotrophs and sensitises them to GnRH ✓
• C Inhibin B is withdrawn, removing negative feedback on FSH specifically
• D Rising LH itself auto-amplifies gonadotroph secretion via short-loop positive feedback

Explanation

Normally GnRH pulsatility is required to prevent receptor downregulation; continuous GnRH causes desensitisation. However, at mid-cycle, rising oestradiol (positive feedback) upregulates GnRH receptors on gonadotrophs and alters post-receptor signalling, rendering gonadotrophs acutely hyperresponsive to the GnRH pulse frequency. This GnRH self-priming effect (mediated by oestrogen) is essential for generating the preovulatory LH surge. Progesterone contributes to the FSH surge after the LH peak but is not the primary sensitising factor at surge onset.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.