TESTOSTERONE

Circulating levels

TESTOSTERONE in the Blood

Sex steroids are transported in blood bound primarily bound to either albumin or Sex Hormone-Binding Globulin (SHBG) or albumin

TESTOSTERONE in plasma exists in two forms:

In Men

(1) NOT available for tissue uptake - SHBG-bound (44-65%) -The plasma level of SHBG (Sex Hormone Binding Globulin) approximately equals TESTOSTERONE levels(~25nm, ~22nM resp.);

(2) Available for tissue uptake - Non-SHBG-bound (33-50%) -    most reversibly bound to albumin; ~4% to cortisol-binding globulin;~2% free / unbound;

In Women

(1) NOT available for tissue uptake - SHBG-bound (66-78%) -   The plasma level of SHBG (Sex Hormone Binding Globulin) approximately equals TESTOSTERONE levels(~25nm, ~22nM resp.);

(2) Available for tissue uptake - Non-SHBG-bound (20-30%) - most reversibly bound to albumin; ~4% to cortisol-binding globulin;~2% free / unbound;

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics (5^th Edition) by Carl A. Burtis, Edward R. Ashwood, David E. Brun, Elsevier Health Sciences,Oct 14, 2012.

An increase in TESTOSTERONE or decrease in SHBG level results in more TESTOSTERONE available for tissue uptake - in contrast,hypogonadal men with diminished gonadal function /low TESTOSTERONE production and those who are hyperthyroid have elevated SHBG.

What Affects Blood TESTOSTERONE Levels?

HIGH TESTOSTERONE LEVELS can be caused by:

-    High TESTOSTERONE production caused by:

•  Low estrogen

•  PCOS (polycystic ovary syndrome)

•  Ovarian cancer

•  Using anabolic steroids - for sports/bodybuilding

•  Quercetin - inred wine, inhibits aromatase (enzyme for estrogen production) thus elevating TESTOSTERONE

•  Antioxidants (vitamin A, and E,zinc, and selenium) - all support TESTOSTERONE production

LOW TESTOSTERONE LEVELS can be caused by:

-    Low TESTOSTERONE production caused by:

•  High level estrogen

•  Smoking

•  Aging - lehdig cells in testes become less sensitive to luteinizing hormone (LH);

•  Chronic illness

•  Delayed puberty

•  Hypopituitarism

•  Prolactinoma

•  Testicular failure in men

 

-    Excessive alcohol consumption - increases estrogen levels in men

-    Obesity - enzyme aromatase in fat tissue converts TESTOSTERONE to ESTRADIOL thus lowering TESTOSTERONE;

-    Chronic high stress - causes TESTOSTERONE to be converted to DHEA

-    Increased SHBG - Steroid Hormone Binding Globulin binds TESTOSTERONE in blood, thus lowering available free TESTOSTERONE;

Reference

Medical Biochemistry by N. V. Bhagavan

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics (5^th Edition) by Carl A. Burtis, Edward R. Ashwood, David E. Brun. Elsevier Health Sciences,Oct 14, 2012

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