Neurokinin 3 receptor antagonism decreases gonadotropin and testosterone secretion in healthy men

Summary

Objective

Patients with mutations of NKB and its receptor show hypogonadotrophic hypogonadism, but there is little evidence for the importance of this pathway in reproductive function in normal men, or its functional hierarchy with kisspeptin.

Design

An open label study wherein men (n=6) were administered the NK3R antagonist MLE4901 40mg orally twice a day for 7 days. Kisspeptin-10 (0.3 μg/kg iv bolus) was given before and on day 7 of NK3R antagonist treatment.

Patients

Subjects were healthy men.

Measurements

Reproductive hormones were measured before and during the NK3R antagonist administration, including frequent sampling on two occasions for analysis of pulsatile LH secretion.

Results

LH, FSH and testosterone secretion were decreased during NK3R antagonist administration. LH showed a biphasic response, being reduced after 24 hours of treatment (4.5±0.6 IU/l pre-treatment to 1.7±0.2 IU/l, p<0.05), with partial recovery thereafter; but it was again decreased on day 7 (2.5±0.6 IU/l, p<0.05 vs pre-treatment). FSH secretion was also suppressed, with a similar temporal pattern to that of LH. Testosterone secretion was decreased from 24 hours (18.4±1.6 pre-treatment vs 5.6±1.5 nmol/l, p<0.01) and remained suppressed throughout the treatment period. Analysis of LH pulsatility showed that both basal and pulsatile LH secretion were markedly suppressed but there was no detected change in LH pulse frequency. Kisspeptin-10 stimulated LH secretion, with similar responses before and during NK3R antagonist administration.

Conclusions

These data demonstrate a central role for NKB/NK3R in the physiological regulation of reproductive function in men, and that this is functionally upstream of kisspeptin-mediated GnRH secretion.

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