560 Obstetrics and Gynecology Board Review •••
❍ How many GnRH receptors are in each pituitary gonadotrope?
10,000 receptors.
❍ What is the structure of GnRH?
GhRh is 10 amino acid decapeptide arranged in a “hair pin” loop.
❍ How is the GnRH delivered to portal circulation?
Via an axonal pathway.
❍ What reproductive hormone measurement is used as an indication of GnRH pulsatility?
Luteinizing hormone (LH).
❍ How is GnRH pulsatility described in the follicular phase?
Pulsatile secretion is more frequent but lower in amplitude during the follicular phase compared with the luteal phase.
❍ How is GnRH pulsatility described in the luteal phase?
Higher amplitude compared with follicular phase. Slower pulsatile secretion, especially toward the end of the luteal
phase, which favors FSH synthesis that is required for the next cycle.
❍ What is the regulatory mechanism responsible for GnRH pulsatility?
Pulsatile, rhythmic activity is an intrinsic property of GnRH neurons, although various hormones and
neurotransmitters modulate that action.
❍ What is the effect of norepinephrine on GnRH pulsatile release?
Stimulatory.
❍ What is the effect of dopamine and serotonin on GnRH pulsatile release?
Inhibitory.
❍ What is the effect of neuropeptide Y on GnRH pulsatile release?
Stimulatory.
❍ What is the effect of melatonin on GnRH pulsatile release?
Inhibitory.
❍ What is the effect of endogenous opiates on GnRH pulsatile release?
Inhibitory.
❍ True or False: Each pulse of LH measured in the peripheral blood corresponds to a hypothalamic pulse of
GnRH into the portal system in a one-to-one relationship.
True. Of note, although FSH is released with LH, FSH pulses are much more difficult to detect because the
half-life of FSH is longer than the interval between GnRH pulses.