Veldhuis, J. D.

SummaryBackgroundGonadotropin‐inhibitory hormone (GnIH, human homologue of RFRP‐3) suppresses gonadotropin secretion in animal models, but its effects have not been studied in the human.ObjectiveWe tested the hypotheses that exogenous GnIH inhibits LH secretion (i) in postmenopausal women and (ii) in men concurrently administered exogenous kisspeptin.DesignFollowing in vitro and in vivo preclinical studies to functionally characterize the GnIH peptide, a dose‐finding study (human GnIH: 1·5–150 μg/kg/h, iv for 3 h) was undertaken, and 50 μg/kg/h selected for further evaluation. Five postmenopausal women were administered 50 μg/kg/h iv infusion for 3 h or vehicle on two separate days. Four men were administered kisspeptin‐10 (0·3 μg/kg iv bolus) with simultaneous infusion of GnIH (50 μg/kg/h, iv for 3 h) or vehicle.ParticipantsHealthy postmenopausal women (mean age 58 ± 2 years, LH: 30·8 ± 2·9 IU/l, FSH: 78·7 ± 6·4 IU/l, oestradiol: <50 pmol/l) and men (39·8 ± 2·1 years, mean total testosterone 12·1 ± 1·8 nmol/l, LH 2·2 ± 0·2 IU/l).Primary outcomeChange in area under curve (AUC) of LH during GnIHvs vehicle.ResultsDuring GnIH administration in postmenopausal women, LH secretion decreased (ΔAUC: −9·9 ± 1·8 IU/3 h) vs vehicle (ΔAUC: −0·5 ± 1·7 IU/3 h; P = 0·02). Kisspeptin‐10‐stimulated LH responses in men were not affected by GnIH co‐administration (60‐min AUC of LH 6·2 ± 0·8 IU/h with kisspeptin‐10 alone, 6·3 ± 1·0 IU/h, kisspeptin‐10 with GnIH, P = 0·72). Exogenous GnIH was well tolerated, with no adverse events reported.ConclusionsGonadotropin‐inhibitory hormone decreased LH secretion in postmenopausal women in this first‐in‐human study. Kisspeptin‐stimulated LH secretion in men was not inhibited during concomitant administration of GnIH.

SummaryTestosterone (T) impacts luteinizing hormone (LH) secretion through negative feedback via the androgen receptor (AR) in the hypothalamo‐pituitary system. An untested postulate is that increasing body mass index (BMI), abdominal visceral fat (AVF) or total abdominal fat (TAF) with ageing decreases LH secretion by heightening T negative feedback via AR. This hypothesis was tested in a prospective, randomized double‐blind cross‐over study of 19 healthy men comparing the effects of flutamide, a selective non‐steroidal AR antagonist and placebo administration on basal and pulsatile LH secretion as a function of age and obesity measures. To this end, serum levels of 2‐hydroxyflutamide (2‐OHF), a major active flutamide metabolite, were measured by mass spectrometry, and AVF/TAF quantified by abdominal computerized tomography. Statistical analysis showed that antiandrogen administration elevated 6‐h mean LH concentrations to 5.4 ± 1.3 IU/L compared with 3.3 ± 1.2 IU/L for placebo (p < 10−3), and total T by 35% (p < 10−4). The LH‐T concentration product doubled (p < 10−8). According to deconvolution analysis, flutamide exposure increased total LH secretion (p < 10−3) and pulsatile LH secretion (p = 0.0077), along with LH pulse frequency (p = 0.019). Despite feedback inhibition, the LH‐T product declined as a linear function of AVF (p = 0.021) and TAF (p = 0.017). This was explained by the fact that higher BMI was associated with lower 2‐OHF concentrations (R = −0.562, p = 0.012). In contrast, age was associated with less pulsatile LH secretion (R = −0.567, p = 0.011) even when LH responses were normalized to antiantrogen levels. In conclusion, increased AVF, TAF and BMI predict decreased LH and flutamide blood levels, whereas older age is marked by impaired stimulation of pulsatile LH secretion even when normalized for antiandrogen levels, suggesting different mechanisms of regulation by adiposity and age.