Hypothalamic-Pituitary-Testicular Axis Disruptions in Older Men Are Differentially Link... - 0 views
press.endocrine.org/...jc.2007-1972
low T low Testosterone low T Testosterone aging LH hormone hormones men male SHBG
shared by Nathan Goodyear on 03 Sep 14
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0.4–2% annual decline
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The core hormonal pattern with increasing age is suggestive of incipient primary testicular dysfunction with maintained total T and progressively blunted free T associated with higher LH.
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Obesity was associated with progressively lower total and free T independent of the simultaneous decrease in SHBG.
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our data highlight the fact that LH was unchanged or even lower in older men in the face of lower T in obesity, suggesting that there may be a failure at the hypothalamic-pituitary level.
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This pattern supports the hypothesis that different underlying mechanisms influence the functions of the HPT axis: age predominantly affects testicular function, whereas obesity impairs hypothalamic/pituitary function.
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the effects of aging on testicular function can be moderated by increased LH compensation for many decades
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obesity impairs hypothalamic/pituitary function independent of age, arguably an adaptive response for which there should be no compensatory mechanism.
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Obesity is associated with insulin resistance (28), and the increased circulating insulin inhibits hepatic SHBG synthesis
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the SHBG increase with age may be related to relative IGF-I deficiency (27), although this has not been directly proven.
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Obesity is associated with peripheral and central insulin resistance (30) and proinflammatory cytokine production (TNFα and IL-6) from adipocytes (31) and central nervous system endocannibinoid release (32), all of which are potential candidates for abrogating hypothalamic endocrine and downstream reproductive axis functions.
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The relationship between obesity and T can be bidirectional: low T may be the cause rather than consequence of obesity
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chronic alcohol abuse is known to suppress LH (40), our data showed no significant association among the three hormones or SHBG and alcohol intake.
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increase in total T in smokers occurs through a primary increase in SHBG with a compensatory rise in LH
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the effects of obesity (BMI or waist circumference) was by far the most important determinant of variance in total T, whereas age per se was important for SHBG, LH, and free T with comorbidity and smoking being comparatively minor contributors
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It is noteworthy that these predisposing lifestyle and health factors are modifiable. This implies that the apparent age-related decline in T may constitute a barometer of health and thus be potentially preventable and/or reversible.
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Age induced decline in Testosterone is more associated with a decline in leydig cell function and thus elevated LH will be associated. In contrast, obesity is more of a HPA axis disruption and thus LH may be normal to low. The pulse amplitude is decrease. No change in pulse frequency is noted. With obesity, a decline in TT and fT was independent of SHBG. Aging is associated with a greater decrease in fT versus TT.