Circulating anti-Müllerian hormone in the older man

This thesis provides the first description of circulating anti-Müllerian hormone (AMH) in older men. AMH is a gonadal hormone, with overt function in the generation of the male phenotype during development, and a biomarker for ovarian reserve in women. AMH is one of four circulating hormones produced by the adult testes, and assumed to have no functional significance in men. Therefore there is an absence of information regarding basic physiology of AMH in the blood of men. This thesis posits that AMH may have cryptic functions, with putative interactions to the other testicular hormones. AMH also belong to the TGF superfamily of cytokines with ubiquitous roles and convergent intracellular signalling in a contexual manner. The role of AMH may become more evident in a model of dysregulated homeostasis, such as that seen with ageing and frailty. This PhD examined a local cohort of 223 men from 19 years to 90 years old for their circulating AMH levels. Three testicular hormones were concurrently examined for interactions with AMH; Inhibin B (InhB), testosterone, and insulin-like peptide 3 (INSL3). The serum profiles of these four hormones were examined throughout the day, and across the age spectrum with a focus on men aged 70 years and older. A small group of older women were also examined for their circulating AMH level to determine for sexual dimorphism with ageing. The extent of cleavage of AMH precursor protein was also studied, and compared between men and boys. A pilot study was concurrently set up to test for the feasibility of correlating AMH and other hormones to functional traits associated with ageing. In healthy young men, circulating AMH and INSL3 levels were both stable throughout the day and independent to each other. This contrasted to the overt diurnal pattern exhibited by testosterone and InhB. Circulating AMH level varies significantly between men, with age-related decline. AMH level was partially correlated to the other Sertoli hormone InhB which became divergent in older men. These findings were concordant with examination of a distinct cohort of older men in the North Island of New Zealand. Both cohorts however had average circulating AMH levels which were lower than a third age-matched cohort of age with healthy cardiovascular status. Circulating AMH was largely sexually dimorphic with ageing, but not invariantly. A minority of older men lacked AMH like all older women. All four circulating testicular hormones are independent in younger men. All four testicular hormones exhibits age-related decline, resulting in multiple combinations of testicular hormonal deficiencies. A minority of older men was deficient in all testicular hormones, similar to all postmenopausal women. The precursor hormone of AMH in blood was strongly linked to its total AMH level. However the extent of its cleavage was distinct to the circulating AMH concentration, and also to the other testicular hormones. AMH was cleaved more in both younger and older men, when compared to boys, with no overlap in their ranges. Amongst men over 70 years, circulating AMH showed a relationship to cognitive function that was highly statistically significant. This was independent to the other testicular hormones. The extent of its cleavage correlated to physical function and weight. AMH is present in the circulation in men, including the oldest old. AMH may play a role as a chronic reporter about the state of the testes that is independent to the other three testicular hormones. This has relevance to the understanding of hypogonadism in the older male

The Daily Profiles of Circulating AMH and INSL3 in Men are Distinct from the Other Testicular Hormones, Inhibin B and Testosterone.

The testes secrete four hormones (anti-Müllerian hormone, insulin-like peptide 3, Inhibin B and testosterone) from two endocrine cell types. It is unknown whether anti-Müllerian hormone and insulin-like peptide 3 levels have a diurnal variation, and if so, whether they covary during the day with testosterone and InhB. Sera were obtained from 13 men at 00:00, 06:00, 09:00, 12:00, 14:00, 17:00 and 19:00 hours and the levels of their testicular hormones measured by ELISA. A second cohort of 20 men was similarly examined with blood drawn at 19:00 and the following 06:00. Anti-Müllerian hormone levels exhibited a subtle diurnal pattern with a 19:00 peak that was 4.9% higher on average than the 06:00 nadir (p = 0.004). The decrease in anti-Müllerian hormone coincided with a rise in testosterone and InhB, but there was no association between the person-to-person variation in the diurnal patterns of anti-Müllerian hormone and testosterone or Inhibin B. Insulin-like peptide 3 had no diurnal pattern, with only minor sporadic variation between time points being observed in some men. In conclusion, the diurnal and sporadic variation of each testicular hormone is distinct, indicating that the major regulation is at the level of the hormone rather than at the endocrine cell type. Consequently, the balance of the hormones being released by the testes has complex variation during the day. The physiological significance of this will vary depending on which combinations of testicular hormones that the target cells respond to

Study 1: diurnal pattern of hormonal expression.

<p>Each individual’s hormone levels were normalised to that individual’s mean across the entire sample period. (A) Sertoli cell hormones: InB (blue circles) and AMH (green triangles); (B) Leydig cell hormones: testosterone (red circles) and INSL3 (orange diamonds); (C) Gonadotropins: LH (brown diamonds) and FSH (pink circle) and (D) Circadian marker: Cortisol. The single 0:00 data point is plotted at both 0:00 and 24:00 with the dashed line used to indicate this extrapolation. The data are the mean ± the standard error of 13 men.</p

Study 1: Daily trend of serum testicular hormones from 13 healthy men plotted individually.

<p>(A) AMH, (B) InhB, (C) INSL3 and (D) testosterone. The 00:00 data points are plotted at both 0:00 and 24:00, with the dashed line used to indicate this extrapolation.</p

Covariation of the diurnal patterns of the hormones.

<p>The covariation between time points for each of the testicular hormones were calculated for 20 men using mixed model analysis, and expressed as the covariation <b>β</b> coefficient (p value). Note that the data is normalised to the daily mean, and is therefore independent of the absolute levels of the men’s hormones.</p><p>* indicates statistical significance.</p><p>Covariation of the diurnal patterns of the hormones.</p

Changes in serum testicular hormonal concentration between 19:00 and 06:00 (Study 2).

<p>(A) AMH, (B) INSL and (C) InhB and (D) testosterone levels were analysed in 20 men. AMH, on average declined by 4.9 ± 1.8%, (p = 0.004, paired Student t-test), whereas the levels of InhB and testosterone increased on average by 28 ± 4% (p<0.0005) and 41% (p = 0.011) respectively. There was no significant change in the levels of INSL3, on average (p = 0.78). The mean levels of the hormones at 19:00 and 06:00 were: AMH (57.9 ± 5.7, 55.0 ± 5.3 pM); InhB (147 ± 13, 189 ± 17 pg/ml); INSL3 (2.28 ± 0.20, 2.21 ± 0.24 ng/ml); testosterone (16.0 ± 1.9, 24.5 ± 2.0 nM).</p

Characteristics of participants in both studies.

<p>The data are the mean ± standard deviation of the 9 am time of day values for study 1 and the 6 am value for Study 2. 1 ng/ml AMH = 7.14 pM.</p><p>Characteristics of participants in both studies.</p

Correction: Elderly Men Have Low Levels of Anti-Müllerian Hormone and Inhibin B, but with High Interpersonal Variation: A Cross-Sectional Study of the Sertoli Cell Hormones in 615 Community-Dwelling Men

The Sertoli cells of the testes secrete anti-Müllerian hormone (Müllerian inhibiting Substance, AMH) and inhibin B (InhB). AMH triggers the degeneration of the uterine precursor in male embryos, whereas InhB is part of the gonadal-pituitary axis for the regulation of sperm production in adults. However, both hormones are also putative regulators of homeostasis, and age-related changes in these hormones may therefore be important to the health status of elderly men. The levels of AMH in elderly men are unknown, with limited information being available about age-related changes in InhB. We have therefore used ELISAs to measure Sertoli cell hormone levels in 3 cohorts of community-dwelling men in New Zealand. In total, 615 men were examined, 493 of which were aged 65 or older. Serum AMH and InhB levels inversely correlated with age in men older than 50 years (p<0.001) but not in the younger men. A minority of elderly men had undetectable levels of AMH and InhB. The variation in hormone levels between similarly aged men increased with the age of men. AMH and InhB partially correlated with each other as expected (r = 0.48, p<0.001). However, the ratio of the two Sertoli hormones varied significantly between men, with this variation increasing with age. Elderly men selected for the absence of cardiovascular disease had AMH levels similar to those of young men whereas their InhB levels did not differ from aged-matched controls. These data suggests that Sertoli cell number and function changes with age, but with the extent and nature of the changes varying between men

Elderly men have low levels of anti-Müllerian hormone and inhibin B, but with high interpersonal variation: a cross-sectional study of the sertoli cell hormones in 615 community-dwelling men.

The Sertoli cells of the testes secrete anti-Müllerian hormone (Müllerian inhibiting Substance, AMH) and inhibin B (InhB). AMH triggers the degeneration of the uterine precursor in male embryos, whereas InhB is part of the gonadal-pituitary axis for the regulation of sperm production in adults. However, both hormones are also putative regulators of homeostasis, and age-related changes in these hormones may therefore be important to the health status of elderly men. The levels of AMH in elderly men are unknown, with limited information being available about age-related changes in InhB. We have therefore used ELISAs to measure Sertoli cell hormone levels in 3 cohorts of community-dwelling men in New Zealand. In total, 615 men were examined, 493 of which were aged 65 or older. Serum AMH and InhB levels inversely correlated with age in men older than 50 years (p<0.001) but not in the younger men. A minority of elderly men had undetectable levels of AMH and InhB. The variation in hormone levels between similarly aged men increased with the age of men. AMH and InhB partially correlated with each other as expected (r = 0.48, p<0.001). However, the ratio of the two Sertoli hormones varied significantly between men, with this variation increasing with age. Elderly men selected for the absence of cardiovascular disease had AMH levels similar to those of young men whereas their InhB levels did not differ from aged-matched controls. These data suggests that Sertoli cell number and function changes with age, but with the extent and nature of the changes varying between men