Androgens Flashcards
What cells synthesize testosterone? What is the precursor to this?
Cells of Leydig
Cholesterol
What are the two general functions of androgens?
Androgenic effects
Metabolic effects
What are the androgenic effects of androgens?
Maturation and continued function of male reproduction
What are the metabolic effects of androgens?
Regulates formation of Muscle, bone, marrow, liver
Describe the HPA axis in regards to the gonadotropes.
GnRH from hypothalamus goes to the pituitary gonadotropes, which release LH and FSH into the blood. These go to the testicular Leydig cells or Sertoli cells.
What are the cells in the pituitary that are stimulated by GnRH? What do they release?
Pituitary gonadotropes
LH and FSH
What is the function of LH in the male? Where does this go?
Stimulates the cells of leydig to secrete Testosterone
What is the function of FSH in the male? Where does this go?
Goes to sertoli cells, to secrete ABP and inhibin
What allows for a higher concentration of LH/FSH in the testicles?
Androgen binding protein
What is the enzyme that is present in the testicles that is not present in the adrenal cortex, and allows for the conversion of androstenedione to testosterone?
17-beta-HSD
What is the function of 5-alpha-reductase?
Converts testosterone into 5-alpha-dihydrotestosterone, a more potent form of testosterone
What is the general way in which GnRH is released from the hypothalamus?
Pulsatile fashion
How does LH increase the production of testosterone?
increasing the expression of cholesterol desmolase
What is the feedback mechanism for LH?
Testosterone inhibits hypothalamus from releasing GnRH
What are the two products of further metabolizing testosterone? What do these do in the HPA axis?
DHT
Estradiol
Inhibit pituitary gonadotropes
Draw out the pathway of cholesterol synthesis.
Draw.
What is the enzyme Leydig cells express that convert androstenedione to testosterone?
17beta-HSD
True or false: testosterone is highly bound to albumin in the blood. What (other) protein is it bound to?
True
Sex hormone binding globulin.
What happens to the amount of sex hormone binding globulin as we age? What is the significance of this?
Decreases, meaning less testosterone circulating as we age.
What is the MOA of testosterone? DHT?
Binds to cytoplasmic receptor, which can then transverse the nucleus, and increase transcription
DHT is the same, but more potent
What is the enzyme that converts testosterone into estradiol?
p450s
What enzyme is found in high concentrations in the prostate? What is the significance of this?
5-alpha-reductase
Increases DHT there
What is the chemical that can freely diffuse into cells, and can then by converted into testosterone? What is the enzyme that does this?
DHEAS
17-beta-HSD
What is the effect of testosterone in the liver in regards to lipids? What is the significance of this?
Increase VLDL and LDL
Decrease
This may be why males have an increased rate of artherosclerosis
What is the effect of testosterone on lipid accumulation in adipocytes?
Inhibits
What is the effect of testosterone on blood glucose levels? How?
Lowers by increasing the expression of glucose transporters on the plasma membrane of adipocytes
What is the effect of testosterone on RBCs?
Increases production of erythropoietin
Why is it that very close monitoring is required when using testosterone replacement therapy in growing children?
May prematurely close the growth plates
What is the gynecological disorder where testosterone is used?
Severe endometriosis
What are the primary causes of hypogonadism? (2)
- Testicular dysfunction (cryptorchidism)
- Klinefelter
What is hypergonadotropic hypogonadism?
Primary cause of hypogonadism with increased levels of GnRH, but low levels of testosterone
What is hypogonadotropic hypogonadism?
Secondary cause of hypogonadism with lowered levels of GnRH, and low testosterone levels
What is methyltestosterone? Route of administration? SIde effects?
-17-alkylated derivative of testosterone
This prevents first pass effect of the liver
-PO
-Causes hepatocellular CA
What is the MOA of testosterone enanthate? Route of administration?
Ester of testosterone that is VERY lipophilic.
Causes slow release and slow metabolism.
IM
What is the route of exogenous testosterone?
Transdermal
What is the two hematological/metabolic side effect of testosterone replacement?
- Polycythemia
- Increased FAs, LDL in circulation
How does exogenous testosterone cause gonadal atrophy?
Causes increased feedback to inhibit FSH/LH production, which lowers endogenous testosterone synthesis
What is the main use of antiandrogens in females?
Hirsutism
What are the four main uses of antiandrogens in makes?
- Precocious puberty
- BPH
- Prostate CA
- Alopecia
What is the general MOA of GnRH agonists/antagonists?
Increase/inhibit LH production by the pituitary
What are the two androgen receptor antagonists?
Flutamide
Bicalutamide
What is the MOA, use, and side effects of: Flutamide?
Competitive antagonist of the androgen receptor
Treat prostate CA
Causes mild gynecomastia, and is mildly hepatotoxic
What is the MOA, use, and side effects of: Bicalutamide?
Competitive antagonist of the androgen receptor
Treat prostate CA
Causes mild gynecomastia, and is mildly hepatotoxic
Why aren’t androgen receptor antagonists used alone? What are the usually used with?
Will cause an increase in LH and FSH production.
Usually given in conjunction with GnRH analogs
What is the MOA, use, and side effects of: Enzalutamide? (3 MOAs)
- Competitively inhibits androgen receptors
- Inhibits the translocation of the nuclear androgen receptor
- Blocks coactivator recruitment
What is the MOA of Leuprolide? Use?
GnRH agonists
Treats prostate CA
What is the MOA of Goserelin? Use?
GnRH agonists
Treats prostate CA
How do GnRH agonists decrease testosterone production?
Constant presence lower the affinity of receptors (although there is an initial increase in LH)
How does the affinity of GnRH agonists compare to physiological GnRH?
Increased binding affinity and decreased proteolysis
What are the side effects of GnRH agonists? (4)
Sexual dysfunction
Osteopenia
Anemia
Fatigue
Why are androgen antagonists coadministered with GnRH agonists?
Prevent the initial surge in testosterone that can lead to prostate CA growth
What is the MOA and use for Degarelix? What is the benefit of this drug over others in its clas?
GnRH receptor antagonist with a faster onset than others, and does NOT cause a testosterone surge
What is the MOA of Abiraterone? Use? Side effects?
Blocks 17-alpha-hydroxylase
Treats metastatic prostate CA
Adrenal insufficiency and hepatotoxic
How does Abiraterone cause hypokalemia and fluid retention?
Inhibiting 17-alpha- hydroxylase production also shunts cholesterol down cortisol production pathway
What is the MOA of Finasteride? Use? Side effects?
Inhibit 5-alpha-reductase, reducing DHT in the prostate
BPH treatment
Impotence and gynecomastia
What is the MOA of Dutasteride? Use? Side effects?
Inhibit 5-alpha-reductase, reducing DHT in the prostate
BPH treatment
Impotence and gynecomastia
What is the causative agent in male pattern baldness?
DHT-there is increased levels of 5-alpha- reductase in baldies
How do high levels of DHT cause baldness?
Induce apoptosis of dermal papilla cells
What is the drug of choice for treating male pattern baldness?
Finasteride (propecia)
Why aren’t 5 alpha reductase inhibitors used in the treatment of prostate CA? (2 reasons)
Worsens high grade CAs
Lowers PSA levels
What are the 3 neurogenic causes of ED?
Neuropathy
Stroke
Spinal cord injury
What are the 2 hormonal causes of ED?
Hypogonadism
Hyperprolactinemia
What are the 3 vasculogenic causes of ED?
Arthrosclerosis
DM
HTN
What are the drugs that can cause ED? (3)
EtOH
Antihypertensives
Antidepressants
What is the MOA of an erection?
Increased NO production, causing increase in cGMP.
This causes relaxation of smooth muscles in the corpus cavernosum
What is the MOA of Sildenafil? Use? Side effects?
Inhibits phosphodiesterase-5 (PDE-5), increasing cGMP levels.
Treats ED
MI (maybe)
What is the MOA of Vardenafil? Use? Side effects?
Inhibits phosphodiesterase-5 (PDE-5), increasing cGMP levels
Treats ED
MI (maybe)
What is the MOA of Tadalafil? Use? Side effects?
Inhibits phosphodiesterase-5 (PDE-5), increasing cGMP levels
Treats ED
MI (maybe)
Which of the PDE5 inhibitors has the longest half-life?
Tadalafil (18 hours)
How are PDE-5 drugs metabolized? What is the significance of this?
Liver p450s, meaning anything that inhibits these will increase duration of action of PDE5s
What is the major drug interaction with PDE5 inhibitors?
Nitrates can cause an unsafe drop in blood pressure
What is the role of the inhibin protein that sertoli cells secrete?
Inhibits pituitary gonadotropes from secreting LH and FSH
What is the feedback mechanism for the gonadotropes on the hypothalamus (1)? Pituitary (4)?
Hypothalamus is inhibited by testosterone
Pituitary is inhibited by testosterone, DHT/E2, and Inhibin
What is the hormone that is responsible for the closure of the epiphyseal growth plates? What is the significance of this in regards to exogenous androgens?
Estradiol
Need to limit use in children
What are the two 5-alpha-reductase inhibitors?
Finasteride
Dutasteride