|dc.description.abstract||Background: Hypothalamic kisspeptin and neurokinin B (NKB) are central
regulators of GnRH and thus gonadotropin (LH and FSH) secretion. Men and
women with loss-of-function mutations in NKB-kisspeptin pathway show
hypogonadotropic pubertal delay with reduced GnRH/LH pulsatility. Studies in
patients with defects in NKB signalling suggest that kisspeptin is functionally
downstream of NKB, although there are very limited data on the relevance of the
NKB pathway in normal men or women, and no hierarchical data on this. The studies
described in this thesis have investigated the interaction between these neuropeptides
in the control of human reproduction in conditions of varying sex-steroid
environment, and in states of fast and slow LH secretion (men, menopause, various
stages across the menstrual cycle).
Overall hypothesis: Pharmacological blockade of NKB signalling will decrease LH
secretion by modulating GnRH/LH pulsatility, indicating the involvement of the
NKB pathway in normal human reproductive function. It is also hypothesised that
this will not abrogate the stimulatory kisspeptin response, revealing a functional
hierarchy whereby NKB signalling is upstream of kisspeptin.
Research strategy: A specific neurokinin-3 receptor antagonist (NK3R antagonist,
AZD4901) was administered 40 mg twice daily orally for 7 days with and without
kisspeptin-10 (KP-10) challenge. Response of reproductive hormones (serum and
urinary where applicable) was measured. LH was sampled every 10 minutes for 8
hours to assess LH pulsatility by blinded deconvolution.
Role of neurokinin B and kisspeptin in healthy men
Six healthy men underwent LH pulsatility study pre-treatment and on day 7 of NK3R
antagonist administration with iv KP-10 bolus (0.3 μg/kg) at 6 hours. NK3R
antagonist reduced LH and testosterone secretion, whilst stimulatory LH response to
KP-10 was unaffected. LH pulse frequency was unchanged by the NK3R antagonist
but basal (nonpulsatile) and pulsatile LH secretion was markedly reduced.
Role of neurokinin B and kisspeptin in postmenopausal women
Eleven postmenopausal women underwent LH pulsatility study pre-treatment and on
day 7 of NK3R antagonist administration with iv KP-10 bolus (0.3 μg/kg) at 6 hours.
NK3R antagonist decreased LH secretion. Basal (nonpulsatile) LH secretion also fell
and while LH pulse frequency did not change in a group as a whole, it did fall in the
8 of 11 postmenopausal womenwith hot flushes. These women reported a reduction
in hot flush frequency (3.4±1.2 vs 1.0± 0.6 flushes/day with NK3Ra, p=0.008) and
severity whilst on NK3R antagonist. LH response to KP-10 was minimal and
unaffected by the NK3R antagonist.
Role of neurokinin B across different phases of menstrual cycle
The effect of NK3R antagonist on ovarian function was compared in early follicular
(n=13), late follicular (n=6) and luteal phase (n=6) to no treatment control cycle.
Early follicular: NK3R antagonist was commenced from cycle day 5-6. The diameter
of the leading follicle was smaller than in controls at the end of treatment (9.3±0.4 vs
15.1±0.9 mm, p<0.0001). Serum estradiol was also reduced and the endometrium
was thinner. Although NK3R antagonist had no effect on LH pulse frequency, basal
(nonpulsatile) LH secretion was decreased, suggesting that NKB modulates GnRH
secretion. After stopping treatment, follicle development resumed and estradiol
secretion increased thereby delaying the LH surge in 11/13 women (LH surge cycle
day 22±1 vs 15±1, p=0.0006). The delayed LH surge and ovulation were confirmed
by a similarly delayed rise in urinary progesterone and prolonged cycle length.
NK3R antagonist did not affect luteal function.
Late follicular: NK3R antagonist was administered from the emergence of a
dominant follicle (≥12mm). Whilst there was an LH surge in all treated cycles,
estrogen feedback was perturbed by the NK3R antagonist, as there was increased
variation in the timing of LH surge compared to control cycle. NK3R antagonist had
no effect on the growth of a dominant follicle and luteal function was unaffected.
Luteal: NK3R antagonist was administered from day +2-3 of the disappearance of
the dominant follicle. NK3R antagonist reduced the variation in the timing of peak
estradiol secretion. Estradiol and progesterone concentrations remained unchanged,
suggesting that luteal function was overall unaffected by this treatment. No
difference in mean LH was observed, although LH pulsatility was not assessed.
Role of neurokinin B and kisspeptin in the mid-cycle LH surge
A model of follicular phase (cycle day 9-11) administration of estradiol (200μg/day)
to induce LH secretion at 48 hours was used in twenty women, mimicking LH
surge. In this model, KP-10 infusion (4μg/kg/hr for 7 hours) enhanced LH secretion,
the response of which was directly correlated with estrogen concentration, indicating
a role of kisspeptin in estrogen feedback. Pre-treatment with NK3R antagonist
decreased LH pulse frequency and whilst the immediate LH response to KP-10 was
unaffected, it blunted the duration of this response and abolished the relationship
between estradiol and kisspeptin-induced LH secretion.
Conclusions: These data indicate the role of NKB-KP pathway in regulating human
reproductive function and that this is via the modulation of pulsatile GnRH secretion.
Whilst NKB is predominantly proximal to kisspeptin, the hierarchy is more complex
than simply linear in the control of human HPG axis. Manipulation of NKB-KP
signalling has therapeutic potential in regulating GnRH/LH secretion in wide range
of clinical settings, including contraception, sex-steroid dependent disorders and in
the treatment of hot flushes.||en
|dc.contributor.sponsor||Medical Research Council (MRC)||en
|dc.publisher||The University of Edinburgh||en
|dc.relation.hasversion||George JT, Kakkar R, Marshall J, Scott ML, Finkelman RD, Ho TW, Veldhuis J, Skorupskaite K, Anderson RA, McIntosh S, Webber L: Neurokinin B Receptor Antagonism in Women With Polycystic Ovary Syndrome: A Randomized, Placebo- Controlled Trial. The Journal of clinical endocrinology and metabolism. 2016;101(11):4313-21.||en
|dc.relation.hasversion||Skorupskaite K, George JT, Anderson RA: The kisspeptin-GnRH pathway in human reproductive health and disease. Human reproduction update. 2014;20(4):485-500.||en
|dc.relation.hasversion||Skorupskaite K, George JT, Veldhuis JD, Millar RP, Anderson RA: Interactions Between Neurokinin B and Kisspeptin in Mediating Estrogen Feedback in Healthy Women. The Journal of clinical endocrinology and metabolism. 2016;101(12):4628- 36.||en
|dc.subject||Gonadotropin Releasing Hormone||en
|dc.title||Kisspeptin and neurokinin B in the regulation of the human hypothalamic-pituitary-gonadal axis||en
|dc.type||Thesis or Dissertation||en
|dc.type.qualificationname||PhD Doctor of Philosophy||en