Neurokinin B Regulates Gonadotropin Secretion, Ovarian Follicle Growth, and the Timing of Ovulation in Healthy Women

Neurokinin B (NKB) is obligate for human puberty, but its role in adult female gonadotropin secretion and ovarian follicle growth is unknown. To investigate antagonism of NKB on pulsatile gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion and ovarian follicle development in healthy women. Open investigation of the effects of a neurokinin-3 receptor (NK3R) antagonist (NK3Ra) vs a no-treatment control cycle. Clinical research facility. Healthy women with regular menses (n = 13). NK3Ra MLE4901 40 mg taken orally twice daily from cycle day 5 to 6 for 7 days. LH secretion, ovarian follicle growth, and timing of ovulation. NK3Ra administration reduced basal LH secretion without a change in pulse frequency and delayed the LH surge by 7 days, the duration of treatment [mean cycle day ± standard error of the mean (SEM), 22 ± 1 days vs 15 ± 1 days in control cycles; P = 0.0006]. Follicle growth (mean diameter at the end of administration of NK3Ra administration ± SEM, 9.3 ± 0.4 mm vs 15.1 ± 0.9 mm in control cycles; P < 0.0001) and rising estradiol concentrations (mean ± SEM, 166 ± 29 pmol/L vs 446 ± 86 pmol/L in control cycles; P < 0.0001) were prevented. After treatment, follicle development resumed and normal preovulatory follicle diameter and estradiol concentrations were demonstrated. Postovulatory progesterone rise was similarly delayed (peak cycle day, 30 ± 2 vs 22 ± 1; P = 0.002) and cycle length was prolonged (35 ± 1 days vs 29 ± 1 days in control cycles; P = 0.0003) but luteal progesterone excretion was unaffected by the NK3Ra (LH surge day +7 mean urinary progesterone levels ± SEM, 58 ± 10 pmol/mol vs 48±7 pmol/mol creatinine in control cycles; nonsignificant). These data demonstrate the involvement of NKB-NK3R signaling in the physiological regulation of GnRH/LH secretion, determining normal follicle development in women.