-Where is testosterone mainly synthesized? What cells?
-In testes and ovaries – Leydig cells
Hypothalamic-Pituitary-Gonadal axis
-Describe this sucker
1) gonadotropin-releasing hormone (GnRH) synthesized and released by hypothalamus
- pulsatile release
2) GnRH binds to gonadotropes=release of lutinizing hormone (LH) + follicle stimulating hormone
3) LH bind leydig cells–> testosterone production + secretin
- testosterone diffuses to sertoli cells=spermatogenesis
- acts on other cells via blood
4) FSH stimulates sertoli cells to produce ABP-androgen binding protein–>concentrates testosterone at the site of spermatogenesis
5) FSH stim sertoli cells to produce inhibin–>inh FSH production @ ant pit
Negative feedback pathways of the Hypothalamic-pit-gonadal axis:
1) Testosterone –> inh ant pituitary release of LH + inh GnRH release by hypothala
2) testosterone and its products converted into 5alhpa-dihydrotestosterone and estradiol –> inh ant pit release of LH
3) FSH stim sertoli cells to produce inhibin–>inh FSH production @ ant pit
What enzyme do LEydig cells have that is different from the adrenal cortex? What does it convert?
- 17beta-hydroxysteroid dehydrogenase (17beta-HSD)
- converts androstenedione to testosterone
Testosterone in the blood…
bound to albumin (weak binding - considered bioavailable) or bound to sex hormone-binding globulin (SHBG-strong binding=not bioavailable)
Testosterone MOA & conversion products:
- binds to intracellular androgen receptor (AR) –> inc or dec gene transcription
- converted to 5alpa-dihydrotestosterone in prostate(DHT)= way hgiher biological activity when bound to AR then - longer t.5
- converted to estradiol by CYP19 (aromatase-in many tissues)
5alpha-Dihydrotestosterone role in male vs testosterone role:
- 5alpha role=dev of penis, scrotum, urethra, prostate, sebum, beard, sperm production,
- testosterone role = epidydimis, vas deferens,
- both do: seminal vesicles, sperm production, penis size
Anabolic effects of androgens:
- stimulates resting metabolic rate
- inh lipid accumulation in adipocytes, stimulates lipolysis, inh differentiation of adipocyte precursors
Androgen effects on skeleton:
- reduces bone reabsorption and enhances bone formation
- testosterone converted to estradiol = estrdiol closes epiphyseal plate (stops bone growth)
Androgen effects on RBC:
-inc erythropoietin production
Androgen effect on muscle:
inc protein synthesis and inh protein breakdown
Primary hypogonadism:
- what happens?
- causes?
1) problem is testicular dysf=dec in testosterone production
- loss of neg feedback=inc in circulating gonadotrophins (hypergonadotropic hypognadsm)
2) Causes: cryptorchidism(undescended testes); kleinfelters; medication (chemo)
Secondary hypogonadism
-what happens?
-problem is w/ hypothalapituitary or morbid obesity
dec is circulating gonadotrophins (hypogonadotropic hypognadsm)
-low testosterone with low LH and FSH
Which hypogonadism has low and which has high levels of circulating gonadotropins?
primary has HYPERGONADOTROPIC hypogonadism bc loss of neg feedback (testicular dysfunction)
secondary has HYPOGONADOTROPIC hypogonadism (hypothala/pit are broken)
relationship bw metabolic syndrome and hypogonadism:
- go hand in hand (obesity+insulin resistance+ hypogonadism)
- testosterone converted to estradiol by adipose
- What does adipose tissue do to testosterone?
- What effect does this have?
- testosterone converted to estradiol by adipose
- estradiol effects–> inh LH release from pit ==> reduced testosterone levels ==> less Testosterone means more adipose and its a viscious cycle
Hypogonadism - what dec leydig cells production of testosterone?
insulin resistance due to adipose tissue
Hypogonadism - what dec hypothala/pit producion of LH (and less LH = dec stimulation of leydig cells to produce testosterone)?
leptin, adipokines, and estradiol from adipose tissue
As we age what happens to free testosterone?
decreases and associated wtih a much of conditionss -prostate cancer -libido -cognition muscle stretngth -mood ...etc
androgen therapeutic uses:
- stimulate sexual dev + inc in height in teens
- repleacement therapy in hypogonadal men
- aging-maintain vitality/vigor, reduce bone loss, sexual dysf
- osteoporosis
- gynecological disorders
- anabolic effects a) debilitated states-AIDS,prolonged immobilization b) athletics
17alpha-alkylated androgen drugs? route of administration?
- methyltestosterone (oral + sublingual)
- fluoxymesterone (oral)
- danzaol (oral)
testosterone ester androgen drugs? route of administration?
(fatty acids added to testosterone)
- testosterone enanthate (IM)
- testosterone cypionate (IM)
-slower metabolism and longer duration
Which androgen drug is administrated as a transdermal/topical gel?
testosterone itself bro
testosterone ester androgen drugs- benefit to use?
- slower metabolism and longer duration
- fatty acid attached = fat soluble = given intramuscular
