Posts Tagged ‘Testosterone’

Dermal Papilla Androgen Sensitivity, Androgen Receptors & Methylation

Thursday, December 30th, 2010

Due to the understanding of male pattern baldness as Androgenic Alopecia (i.e. as an androgen-dependent process), many studies have focused on androgen metabolism (AM) in the body and how androgens effect hair.  Studies have shown that “all dermal papilla cells from androgen-sensitive sites contain low capacity, high affinity androgen receptors.” [18]

The dermal papilla (DP), at the base of the hair follicle, has androgen receptors (AR’s) that androgens from the blood bind to. In androgen-sensitive follicles, the androgens are synthesized and diffused over small distances; this induces changes in neighboring cells (like keratinocytes cells) in what is known as “paracrine interactions”. The diffusible proteins are called paracrine factors. [18]

When beard and scalp cells were incubated in androgens, androgens stimulated the cells’ ability to triggered mitosis (cell division) in beard cells but not in scalp cells. The interesting outcome here was that incubation with androgens had the exact opposite effect on scalp cells; these (scalp) cells’ mitogenic capacity was inhibited. [18]

Androgen-sensitive follicles are not simply targeted and affected by androgens; they are actually involved in androgen metabolism (AM) and can convert androgens using steroid-producing (steroidogenic) enzymes, also known as intrafollicular steroidogenic enzymes. [25]

A 2004 study shed more light on specific processes that shorten the hair cycle (that occur within the DP). According to the study, the three processes are as follows: “(1) the conversion of testosterone to DHT by type II 5-alpha-reductase; (2) the synthesis of TGF-beta2 in dermal papilla cells; and (3) the activation of the intrinsic caspase network.” [6]

The research seems to indicate AM activity at the DP of the hair follicle, amongst other interactions is not fully understood yet. Some of the known intrafollicular steroidogenic enzymes found in the DP are: Steroid Sulfatase (STS), 17beta-hydroxysteroid dehydrogenases (17b-HSD), 3beta-hydroxysteroid dehydrogenases (3b-HSD)  and type 1 and 2 5alpha-reductase (type 1 and type 2 5alpha-R). Type 2 5-alpha-reductase has been the target of a number of studies that showed it to accelerate the conversion of free testosterone into DHT. [10] [11] [12] [24] [25] [28] [31]

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Free Testosterone

Thursday, December 30th, 2010

The levels of free testosterone (free T) and the type 2 5alpha-reductase enzyme in serum has been the target of research; there seems to exist a strong coloration between the levels of available free testosterone in serum of the human body and baldness. [21] [23]

A 1997 study found that “several strong associations also were found between hormone levels and hair patterning.” This study found that “men with vertex and frontal baldness had higher levels of free T”. [2]

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It is also known that both 5alpha-reductase enzymes types 1 and 2 convert testosterone (T) to dihydrotestosterone (DHT) as mentioned earlier, [4] particularly type 2.

Should the Term “Androgenic Alopecia” Be Used? (Research History)

Wednesday, December 29th, 2010

About 60 years ago Hamilton made an important observation when he noticed that castrated men did not have AGA. He concluded that hair growth on the scalp was androgen-dependent.

Despite androgens causing hair loss in many men, androgens are actually crucial as they are responsible for the development of puberty; they also aid in, if not cause, male maturation, growth of muscles and the appearance of other sexual characteristics in young humans. [25]

Androgens, such as testosterone (T) and dihydrotestosterone (DHT), have been identified by researchers to be the main regulators of hair growth. Androgens contribute to the changing of vellus (tiny, un-pigmented) hairs into terminal (thicker) hair follicles. [18]

Paradoxically, androgens are also are often thought of as the main culprit behind male pattern baldness.

Androgens in the scalp of adults with androgen-dependent hair follicles seem to have two undesirable effects. The first being that they shorten the anagen phase (long growth phase). [6]

A study published in November 2002 further explained that the follicles experience a “transformation from long growth (anagen) and short rest (telogen) cycles, to long rest and short growth cycles.”  [3]

The second effect always accompanies the first and maybe the manifestation of it. This effect is manifested as the gradual changing of (thick) terminal hair follicles to (thinner) vellus hair (due to the reduction of the cellular hair matrix volume). This change in thickness has been referred to as a “progressive miniaturisation of the follicle.”[3] [5] [18] [23]

In summary, androgens shorten the long growth cycle (anagen phase) and cause follicles to enter into the resting cycle (telogen phase) faster and remain in that phase longer; this results in finer and finer hair. This process  is what we’ve identified as, or termed, AGA.

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J Am Acad Dermatol. 1999 Feb;40(2 Pt 1):200-3. “Hormones and hair patterning in men: a role for insulin-like growth factor 1?”

Wednesday, August 18th, 2010

-::- Note: The below is published here for archival purposes -::-

J Am Acad Dermatol. 1999 Feb;40(2 Pt 1):200-3.

Hormones and hair patterning in men: a role for insulin-like growth factor 1?

Signorello LB, Wuu J, Hsieh C, Tzonou A, Trichopoulos D, Mantzoros CS.

Department of Epidemiology and Harvard Center for Cancer Prevention, Harvard School of Public Health, Boston, Massachusetts 02115, USA.

Abstract

BACKGROUND: Androgens are important in hair growth and patterning, whereas growth hormone substitution enhances their effect in growth hormone-deficient men. No previous study has jointly evaluated the function of sex steroids, sex hormone-binding globulin (SHBG), and insulin-like growth factor (IGF-1) in determining hair patterning in men.

OBJECTIVE: We assessed the relationship between circulating hormone measurements and both head and chest hair patterning in a sample of elderly men.

METHODS: Fifty-one apparently healthy men older than 65 years of age were studied cross-sectionally. Head and chest hair patterning was assessed by a trained interviewer. Morning blood samples from all subjects were used for measurements of testosterone, estradiol, dehydroepiandrosterone sulfate, SHBG, and IGF-1.

RESULTS: Results were obtained from logistic regression models, adjusting simultaneously for all the measured hormones and age. Men with higher levels of testosterone were more likely to have vertex baldness (odds ratio [OR] = 2.5, 95% confidence interval [CI: 0.9 to 7.8] per 194 ng/dL increment of testosterone). In addition, for each 59 ng/mL increase in IGF-1, the odds of having vertex baldness doubled (95% CI [1.0 to 4.6]). Those who were found to have higher circulating levels of SHBG were less likely to have dense hair on their chest (OR = 0.4, 95% CI [0.1 to 0.9] per 24 nmol/L increment in SHBG]).

CONCLUSION: Testosterone, SHBG, and IGF-1 may be important in determining hair patterning in men.

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