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Nathan Goodyear

The Use of a Sensitive Equilibrium Dialysis Method for the Measurement of Free Testoste... - 0 views

jcem.endojournals.org/...1312.abstract

equilibrium dialysis testosterone free hormone hormones

shared by Nathan Goodyear on 16 Nov 12 - No Cached
  • Nathan Goodyear on 16 Nov 12
     
    evaluation via equilibrium dialysis found free testosterone in men to be only 2-3% with these levels being even smaller in women.  
Nathan Goodyear

Testosterone and Abnormal Glucose Metabolism in an Inner-City Cohort - 0 views

www.ncbi.nlm.nih.gov/...PMC3809764

low T testosterone methadone narcotics

shared by Nathan Goodyear on 05 Nov 13 - No Cached
  • Nathan Goodyear on 05 Nov 13
     
    This study of inner city men found low T associated with methadone use.  Narcotics are a known risk factor for low T.  The free T was calculated from serum.  This equilibrium dialysis is based on too many variables.  Look at the studies on equilibrium dialysis.  This study also found calculated free T was not associated with insulin resistance.  However, insulin resistance is a peripheral tissue dysfunction not a serum dysfunction.  So, a calculated free T (not reality) in the serum shows me nothing of the peripheral activity.  For example, inflammation has been shown to increase aromatase activity in the prostate tissue only.  The thinking in the conclusions of so many of these studies is soooo flawed.
Nathan Goodyear

Free Testosterone Measurement by the Analog Displacement Direct Assay: Old Concerns and... - 0 views

www.clinchem.org/...458.full

free testosterone equilibrium dialysis hormone hormones

shared by Nathan Goodyear on 16 Nov 12 - No Cached
  • Nathan Goodyear on 16 Nov 12
     
    the standard technique of "free testosterone" calculation today is via equilibrium dialysis.  This article describes the problem with current evaluation techniques of current free testosterone evaluation: "this method, although sensitive and reproducible, is cumbersome and not easily adaptable to automated methods".  Most values of "free testosterone" today are either calculated or estimated as this article points out.  Why not just measure with saliva?!
Nathan Goodyear

Are There Variances of Calculated... [Endocr Pract. 2013 March-April 1] - PubMed - NCBI - 0 views

www.ncbi.nlm.nih.gov/...23543029

SHBG albumin equilibrium dialysis free testosterone

shared by Nathan Goodyear on 22 Apr 13 - No Cached
  • Nathan Goodyear on 22 Apr 13
     
    SHBG and albumin shown to be quite variable in the equilibrium dialysis calculation of free testosterone from blood.
Nathan Goodyear

Comparison of salivary versus serum testos... [Menopause. 2009 Jul-Aug] - PubMed - NCBI - 0 views

www.ncbi.nlm.nih.gov/...19325500

saliva salivary hormones hormone testosterone serum testing postmenopausal women menopause

shared by Nathan Goodyear on 30 Oct 12 - No Cached
  • Nathan Goodyear on 30 Oct 12
     
    this study looked at salivary testosterone to serum testosterone and found poor correlation.  One major problem with this study is the significantly smaller amount (10 fold) of testosterone in women than men in healthy individuals.  This study took place in postmenopausal women, which would have significantly lower levels than healthy women.  They also don't discuss the pitfalls of equilibrium dialysis of serum free testosterone.  Another major flaw is the mere logic of looking at serum for tissue activity.   What is the correlation between serum levels and tissue activity.  There is tremendous assumptions being undertaken that serum levels of testosterone whether total or free translate to genomic or non-genomic signaling.  I also wonder if newer techniques using Mass Spec can better detect the typically pico levels of testosterone in women's saliva?  This study does nothing to dissuade the use of salivary testing.
Nathan Goodyear

Morning free and total testosterone in HIV-infected men: implications for the assessmen... - 0 views

www.ncbi.nlm.nih.gov/...PMC3900935

free Testosterone HIV men hormone hormones male SHBG

shared by Nathan Goodyear on 03 Feb 14 - No Cached
  • Nathan Goodyear on 03 Feb 14
     
    low T is found in 20-70% of men with HIV.  What is interesting about this article is that Total Testosterone was found to be a poor assessment of biological active Testosterone.  Free Testosterone assessed in the am was shown to be a better functional assessment in these men.  Serum is a poor choice though.  The process of equilibrium dialysis to calculate free Testosterone is filled with variables that will effect reliability.  Increases SHBG was found associated.
Nathan Goodyear

Predictive accuracy and sources of variabil... [Ann Clin Biochem. 2009] - PubMed - NCBI - 0 views

www.ncbi.nlm.nih.gov/...19225026

equilibrium dialysis free testosterone TT testosterone SHBG

shared by Nathan Goodyear on 11 Jun 13 - No Cached
  • Nathan Goodyear on 11 Jun 13
     
    Study finds variations in calculated free testosterone.  Most of the variability is from the total testosterone, lesser due to the formulas, and third to the SHBG assay.  The point here, is there are too many variables to place a lot of weight on calculated free T in serum. Jus test it in the saliva.
Nathan Goodyear

Redefining Metabolic Syndrome in Men (July 2012) Townsend Letter for Doctors & Patients - 0 views

www.townsendletter.com/...metsyndrome0712.html

testosterone male men hormone hormones saliva salivary low T low metabolic syndrome MetS

shared by Nathan Goodyear on 28 Aug 12 - No Cached
  • Approximately 95% to 98% of testosterone is bound to a carrier protein at any given time, leaving just the remaining 2% to 5% as completely unbound and available for tissues to use
  • most serum laboratories offer a free testosterone level, which is a calculated value based on SHBG levels or determined with equilibrium dialysis
  • the hormone enters the salivary gland by passive diffusion
  • ...11 more annotations...
  • Testosterone has a known age-related decline, and total levels typically drop by approximately 1.6% per year beginning for most men in their 30s
  • As estrogen levels rise, they prompt the body to produce more SHBG, which in turn has a higher binding affinity for testosterone, and drives the unbound fraction of the testosterone pool down even further
  • When the increase in SHBG is taken into account, the age-related decline in the level of hormone that can be used by the body is closer to 2% to 3% per year.
  • Stinging nettle (Urtica dioica), an herb commonly used for allergies, can also be employed to bind to SHBG, which leaves more testosterone available to tissues
  • Leptin, an adipose-derived peptide hormone that regulates appetite and metabolism, has been shown to directly inhibit testosterone production in animal models
  • tumor necrosis factor alpha (TNF-alpha) and interleukin-1 (IL-1) further inhibit Leydig cell testosterone production
  • Natural aromatase inhibitors include the bioflavonoids chrysin and luteolin
  • Zinc deficiency causes an upregulation of the aromatase enzyme
  • Testosterone reduces lipoprotein lipase (LPL) activity
  • there are several herbs that can work to boost testosterone levels, including longjack (Eurycoma longifolia), horny goat weed (Epimedium grandiflorum), and tribulus (Tribulus terrestris).
  • the majority of the hormone is bound to carrier proteins including sex hormone binding globulin (SHBG) and albumin
  • Nathan Goodyear on 28 Aug 12
     
    nice and short review on testosterone and men's  health.
Nathan Goodyear

http://press.endocrine.org/doi/pdf/10.1210/jc.2014-1872 - 0 views

press.endocrine.org/...jc.2014-1872

low T Testosterone treatment therapy diabetes obesity men male hormone hormones

shared by Nathan Goodyear on 29 Jul 14 - No Cached
  • Nathan Goodyear on 29 Jul 14
     
    New study finds Testosterone therapy provides less than statistical significant improvement in constitutional/sexual symptoms, in obese men with type II diabetes with symptoms classified as mild-moderate with modest reductions in Total Testosterone.  This study highlights that low Testosterone is a biomarker of poor health and multiple comorbidities and that simply adding in Testosterone therapy will not cure all male woes.  The authors did state that ED and low T are separate issues and I will differ with them on this--they are in fact link.  This association may vary between individuals, but to flatly state they are completely separate issues is devoid of the fact that testosterone has been shown to reduce inflammatory cytokines and improve PDE5 therapy.  
Nathan Goodyear

Testosterone for the aging male; current evidence and recommended practice - 0 views

www.ncbi.nlm.nih.gov/...PMC2544367

leptin Testosterone low T low Testosterone male hormone hormones

shared by Nathan Goodyear on 27 Oct 14 - No Cached
  • Total serum testosterone consists of free testosterone (2%–3%), testosterone bound to sex hormone binding globulin (SHBG) (45%) and testosterone bound to other proteins (mainly albumin −50%)
  • Testosterone binds only loosely to albumin and so this testosterone as well as free testosterone is available to tissues and is termed bioavailable testosterone
  • Testosterone bound to SHBG is tightly bound and is biologically inactive
  • ...13 more annotations...
  • Bioavailable and free testosterone are known to correlate better than total testosterone with clinical sequelae of androgenization such as bone mineral density and muscle strength
  • peak levels seen in the morning following sleep, which can be maintained into the seventh decade
  • Samples should always be taken in the morning before 11 am
  • The reliable measurement of serum free testosterone requires equilibrium dialysis. This is not appropriate for clinical use as it is very time consuming and therefore expensive.
  • With increasing age, a greater number of men have total testosterone levels just below the normal range or in the low-normal range. In these patients total testosterone can be an unreliable indicator of hypogonadal status.
  • It is advised that at least two serum testosterone measurements, taken before 11 am on different mornings, are necessary to confirm the diagnosis.
  • Patients with serum total testosterone consistently below 8 nmol/l invariably demonstrate the clinical syndrome of hypogonadism and are likely to benefit from treatment. Patients with serum total testosterone in the range 8–12 nmol/l often have symptoms attributable to hypogonadism and it may be decided to offer either a clinical trial of testosterone treatment or to make further efforts to define serum bioavailable or free testosterone and then reconsider treatment. Patients with serum total testosterone persistently above 12 nmol/l do not have hypogonadism and symptoms are likely to be due to other disease states or ageing per se so testosterone treatment is not indicated.
  • Total testosterone levels fall at an average of 1.6% per year whilst free and bioavailable levels fall by 2%–3% per year.
  • With advancing age there is also a reduction in androgen receptor concentration in some target tissues and this may contribute to the clinical syndrome of LOH
  • Metabolic clearance declines with age
  • Gonadotrophin levels rise during aging (Feldman et al 2002) and testicular secretory responses to recombinant human chorionic gonadotrophin (hCG) are reduced
  • There are changes in the lutenising hormone (LH) production which consist of decreased LH pulse frequency and amplitude, (Veldhuis et al 1992; Pincus et al 1997) although pituitary production of LH in response to pharmacological stimulation with exogenous GnRH analogues is preserved
  • the decreases in testosterone levels with aging seem to reflect changes at all levels of the hypothalamic-pituitary-testicular axis
  • Nathan Goodyear on 27 Oct 14
     
    Leptin inhibits male Testosterone production at the level of the hypothalamus and at the testicle level.
Nathan Goodyear

Testosterone and glucose metabolism in men: current concepts and controversies - 1 views

joe.endocrinology-journals.org/...R37.full

Low T Testosterone metabolic syndrome MetS Diabetes men male glucose hormone hormones g

shared by Nathan Goodyear on 04 Feb 14 - No Cached
  • Around 50% of ageing, obese men presenting to the diabetes clinic have lowered testosterone levels relative to reference ranges based on healthy young men
  • The absence of high-level evidence in this area is illustrated by the Endocrine Society testosterone therapy in men with androgen deficiency clinical practice guidelines (Bhasin et al. 2010), which are appropriate for, but not specific to men with metabolic disorders. All 32 recommendations made in these guidelines are based on either very low or low quality evidence.
  • A key concept relates to making a distinction between replacement and pharmacological testosterone therapy
  • ...59 more annotations...
  • The presence of symptoms was more closely linked to increasing age than to testosterone levels
  • Findings similar to type 2 diabetes were reported for men with the metabolic syndrome, which were associated with reductions in total testosterone of −2.2 nmol/l (95% CI −2.41 to 1.94) and in free testosterone
  • low testosterone is more predictive of the metabolic syndrome in lean men
  • Cross-sectional studies uniformly show that 30–50% of men with type 2 diabetes have lowered circulating testosterone levels, relative to references based on healthy young men
  • In a recent cross-sectional study of 240 middle-aged men (mean age 54 years) with either type 2 diabetes, type 1 diabetes or without diabetes (Ng Tang Fui et al. 2013b), increasing BMI and age were dominant drivers of low total and free testosterone respectively.
  • both diabetes and the metabolic syndrome are associated with a modest reduction in testosterone, in magnitude comparable with the effect of 10 years of ageing
  • In a cross-sectional study of 490 men with type 2 diabetes, there was a strong independent association of low testosterone with anaemia
  • In men, low testosterone is a marker of poor health, and may improve our ability to predict risk
    • Nathan Goodyear
      Nathan Goodyear on 04 Feb 14
       
      probably the most important point made in this article
  • low testosterone identifies men with an adverse metabolic phenotype
  • Diabetic men with low testosterone are significantly more likely to be obese or insulin resistant
  • increased inflammation, evidenced by higher CRP levels
  • Bioavailable but not free testosterone was independently predictive of mortality
  • It remains possible that low testosterone is a consequence of insulin resistance, or simply a biomarker, co-existing because of in-common risk factors.
  • In prospective studies, reviewed in detail elsewhere (Grossmann et al. 2010) the inverse association of low testosterone with metabolic syndrome or diabetes is less consistent for free testosterone compared with total testosterone
  • In a study from the Framingham cohort, SHBG but not testosterone was prospectively and independently associated with incident metabolic syndrome
  • low SHBG (Ding et al. 2009) but not testosterone (Haring et al. 2013) with an increased risk of future diabetes
  • In cross-sectional studies of men with (Grossmann et al. 2008) and without (Bonnet et al. 2013) diabetes, SHBG but not testosterone was inversely associated with worse glycaemic control
  • SHBG may have biological actions beyond serving as a carrier protein for and regulator of circulating sex steroids
  • In men with diabetes, free testosterone, if measured by gold standard equilibrium dialysis (Dhindsa et al. 2004), is reduced
    • Nathan Goodyear
      Nathan Goodyear on 04 Feb 14
       
      expensive, laborious process filled with variables
  • Low free testosterone remains inversely associated with insulin resistance, independent of SHBG (Grossmann et al. 2008). This suggests that the low testosterone–dysglycaemia association is not solely a consequence of low SHBG.
  • Experimental evidence reviewed below suggests that visceral adipose tissue is an important intermediate (rather than a confounder) in the inverse association of testosterone with insulin resistance and metabolic disorders.
  • testosterone promotes the commitment of pluripotent stem cells into the myogenic lineage and inhibits their differentiation into adipocytes
  • testosterone regulates the metabolic functions of mature adipocytes (Xu et al. 1991, Marin et al. 1995) and myocytes (Pitteloud et al. 2005) in ways that reduce insulin resistance.
  • Pre-clinical evidence (reviewed in Rao et al. (2013)) suggests that at the cellular level, testosterone may improve glucose metabolism by modulating the expression of the glucose-transported Glut4 and the insulin receptor, as well as by regulating key enzymes involved in glycolysis.
  • More recently testosterone has been shown to protect murine pancreatic β cells against glucotoxicity-induced apoptosis
  • Interestingly, a reciprocal feedback also appears to exist, given that not only chronic (Cameron et al. 1990, Allan 2013) but also, as shown more recently (Iranmanesh et al. 2012, Caronia et al. 2013), acute hyperglycaemia can lower testosterone levels.
  • There is also evidence that testosterone regulates insulin sensitivity directly and acutely
  • In men with prostate cancer commencing androgen deprivation therapy, both total as well as, although not in all studies (Smith 2004), visceral fat mass increases (Hamilton et al. 2011) within 3 months
  • More prolonged (>12 months) androgen deprivation therapy has been associated with increased risk of diabetes in several large observational registry studies
  • Testosterone has also been shown to reduce the concentration of pro-inflammatory cytokines in some, but not all studies, reviewed recently in Kelly & Jones (2013). It is not know whether this effect is independent of testosterone-induced changes in body composition.
  • the observations discussed in this section suggest that it is the decrease in testosterone that causes insulin resistance and diabetes. One important caveat remains: the strongest evidence that low testosterone is the cause rather than consequence of insulin resistance comes from men with prostate cancer (Grossmann & Zajac 2011a) or biochemical castration, and from mice lacking the androgen receptor.
  • Several large prospective studies have shown that weight gain or development of type 2 diabetes is major drivers of the age-related decline in testosterone levels
  • there is increasing evidence that healthy ageing by itself is generally not associated with marked reductions in testosterone
  • Circulating testosterone, on an average 30%, is lower in obese compared with lean men
  • increased visceral fat is an important component in the association of low testosterone and insulin resistance
  • The vast majority of men with metabolic disorders have functional gonadal axis suppression with modest reductions in testosterone levels
  • obesity is a dominant risk factor
  • men with Klinefelter syndrome have an increased risk of metabolic disorders. Interestingly, greater body fat mass is already present before puberty
  • Only 5% of men with type 2 diabetes have elevated LH levels
  • inhibition of the gonadal axis predominantly takes place in the hypothalamus, especially with more severe obesity
  • Metabolic factors, such as leptin, insulin (via deficiency or resistance) and ghrelin are believed to act at the ventromedial and arcuate nuclei of the hypothalamus to inhibit gonadotropin-releasing hormone (GNRH) secretion from GNRH neurons situated in the preoptic area
  • kisspeptin has emerged as one of the most potent secretagogues of GNRH release
  • hypothesis that obesity-mediated inhibition of kisspeptin signalling contributes to the suppression of the HPT axis, infusion of a bioactive kisspeptin fragment has been recently shown to robustly increase LH pulsatility, LH levels and circulating testosterone in hypotestosteronaemic men with type 2 diabetes
  • A smaller study with a similar experimental design found that acute testosterone withdrawal reduced insulin sensitivity independent of body weight, whereas oestradiol withdrawal had no effects
  • suppression of the diabesity-associated HPT axis is functional, and may hence be reversible
  • Obesity and dysglycaemia and associated comorbidities such as obstructive sleep apnoea (Hoyos et al. 2012b) are important contributors to the suppression of the HPT axis
  • weight gain and development of diabetes accelerate the age-related decline in testosterone
  • Modifiable risk factors such as obesity and co-morbidities are more strongly associated with a decline in circulating testosterone levels than age alone
  • 55% of symptomatic androgen deficiency reverted to a normal testosterone or an asymptomatic state after 8-year follow-up, suggesting that androgen deficiency is not a stable state
  • Weight loss can reactivate the hypothalamic–pituitary–testicular axis
  • Leptin treatment resolves hypogonadism in leptin-deficient men
  • The hypothalamic–pituitary–testicular axis remains responsive to treatment with aromatase inhibitors or selective oestrogen receptor modulators in obese men
  • Kisspeptin treatment increases LH secretion, pulse frequency and circulating testosterone levels in hypotestosteronaemic men with type 2 diabetes
  • change in BMI was associated with the change in testosterone (Corona et al. 2013a,b).
  • weight loss can lead to genuine reactivation of the gonadal axis by reversal of obesity-associated hypothalamic suppression
  • There is pre-clinical and observational evidence that chronic hyperglycaemia can inhibit the HPT axis
  • in men who improved their glycaemic control over time, testosterone levels increased. By contrast, in those men in whom glycaemic control worsened, testosterone decreased
  • testosterone levels should be measured after successful weight loss to identify men with an insufficient rise in their testosterone levels. Such men may have HPT axis pathology unrelated to their obesity, which will require appropriate evaluation and management.
  • Nathan Goodyear on 04 Feb 14
     
    Article discusses the expanding evidence of low T and Metabolic syndrome.
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