Reproductive Endocrinology in the Male

Question 1

How did researchers discover that development of the male genitalia occurs by paracrine signaling?

Answer 1

Experiments showed that unilateral removal of a male gonad led female gonadal development on that side only.

Question 2

The Sertoli cells serve as a blood-sperm barrier. One reason is that the spermatozoa need to be protected from toxins in the blood. What is another reason?

Answer 2

To protect the sperm –which develop in puberty –from autoimmune attack (which develops in utero)

Question 3

What does StAR stand for?

Answer 3

Steroid Acute Regulatory protein

Question 4

Leydig cells release testosterone in response to activation of a ____________ receptor.

Answer 4

G-protein coupled

FSH also binds to a GPCR.

Question 5

Testosterone from Leydig cells works synergistically with FSH to increase the expression of _____________ in Sertoli cells.

Answer 5

androgen-binding protein

Question 6

An athlete tests positive for hCG. What’s going on?

Answer 6

He’s taking hCG exogenously!

First, this athlete had been taking anabolic steroids, such as testosterone. Abusive levels are 1,000 times the physiologic levels, so anabolic steroids will shut down the HPA axis. If you know you’re going to be tested soon, then you can stop taking the abusive levels of testosterone. Doing so, however, will lead to complete absence of testosterone which will let authorities know you’re using testosterone.

So, the athlete stopped taking abusive testosterone and supplemented with hCG which closely mimics LH. This stimulates the production of testosterone.

Question 7

Why do those who abuse testosterone have azoospermia?

Answer 7

Because exogenous testosterone will shut down the normal gonadotrophic system (there’s more to this… look up lecture notes from the Panoptoed session and fill out)

Question 8

Many anti-estrogen drugs were recently added to the banned substances list due to ___________________.

Answer 8

their potential use as drugs that hide gynecomastia

Question 9

Why do men with lots of testosterone end up shorter?

Answer 9

Because testosterone stimulates bone maturation

Question 10

The Wolffian duct develops in the presence of ____________.

Answer 10

testosterone

Question 11

True or false: estrogen from the ovaries is needed for proper development of the Müllerian system.

Answer 11

False. The Müllerian system develops independent of gonadal hormones. (In fact, this is why those with Turner syndrome will have normal vagina, uterus, and fallopian tubes even in the absence of ovaries.)

Question 12

In males, where does testosterone get metabolized to estrogen?

Answer 12

Sertoli cells

Question 13

Biochemically, what does LH do to Leydig cells?

Answer 13

It stimulates StAR and over enzymes needed for steroidogenesis.

Question 14

LH and FSH stimulate GPCRs. Ultimately, how does this achieve the necessary hormone effects?

Answer 14

Both hormones bind to Gs receptors which activate PKA. PKA then turns on genes for expression of effector enzymes.

Question 15

Activated Sertoli cells also activate and nourish ___________.

Answer 15

Leydig cells

Question 16

Inhibins do what to Leydig cells?

Answer 16

They stimulate them. (Sertoli cells secrete TGF and IGF which also promote Leydig cells.)

Question 17

One of the reasons females don’t experience as much of a growth spurt as males is that _________________.

Answer 17

estrogen antagonizes GH

Question 18

How does the GH/IGF cycle interact with the GnRH/gonadal cycle?

Answer 18

IGF stimulates the secretion of GnRH, and, in turn, testosterone stimulates the secretion of IGF and GH.

Question 19

True or false: non-aromatized testosterone stimulates bone growth.

Answer 19

False. Only estrogen promotes bone growth and maturation.