Local and systemic control of gonadal function

Human: 1 oocyte – 150 million sperm

0

60

120

180

240

300

0 13

25

38

51

64

76

89

10

2

11

5

12

7

14

0

VISIT NUMBER

CO

NC

EN

TR

AT

ION

1990199119921993

Semen analysis results vary considerablyeven in the normal fertile population.

CONSECUTIVE SEMEN DONORCONCENTRATIONS OVERFOUR YEARS

Cooper T G et al. Hum. Reprod. Update 2010;16:231-245

© World Health Organization [2009]. All rights reserved. The World Health Oragnization has granted Oxford University Press permission for the reproduction of this article

The association of age and semen quality in healthy men B.Eskenazi Human Reproduction Vol.18, pp. 447-454, 2003

Semen volume

Concentration

Count

Motility

Progressive motility

20 40 60 80 20 40 60 80

The likelihood of semen sample being graded as “clinically” abnormal or

unhealthy:

Age22 25%30 40%40 60%60 85%

So where are we going now?

So many sperm? Why? How?Environmental pollutants and male fertility?

3. Cervical mucus.a) penetration characteristicsb) “filter” for immotile sperm1. Human: Vaginal

deposition of semen

2. Human: 99% of sperm lost through retrograde transport

150,000,000

3. Cervical mucus.a) penetration characteristicsb) “filter” for immotile sperm1. Human: Vaginal

deposition of semen

2. Human: 99% of sperm lost through retrograde transport

4. Transport through uterus; phagocytosis

150,000,000

Dog sperm in contact with uterine epithelial cells

Courtesy: Gary England

3. Cervical mucus.a) penetration characteristicsb) “filter” for immotile sperm1. Human: Vaginal

deposition of semen

2. Human: 99% of sperm of sperm lost through retrograde transport

4. Transport through uterus due to muscular contractions; phagocytosis

5. Utero-tubal junction

6. Fallopian tube

150,000,000

The journey?

2. Human: 99% of sperm of sperm lost through retrograde transport

5. Utero-tubal junction

6. Fallopian tube

Sperm bound to ciliated epithelial cells – slow release

Spermatogenesis: How much do you need?

Body weight: 44 kg

Testis size: 120 gm

Body weight: 170 kg

Testis size: 30 gm

Many males mate with same female:

competition!

i.e. 16 x more testicular tissue/kg body wt

Take home message: the more testicular tissue, the more sperm.

Body weight

Tes

tis

wei

ght Man

Multi-male breeding system

Monogamous

~ 8 cm

Why so many sperm?

50 um/sec = 3 mm/min = ~30 min

Take home message: variability in reproduction often correlates withcompetition between males/sperm

Stahlberg et al (2000) pig experiment

0

10

20

30

40

50

60

70

Boar A Boar B

Number ofembryos

% Siredoffspring

• Semen from 2 boars was pooled in equal numbers and inseminated (32 females)

• DNA analysis was used to identify paternity of offspring and embryos

Theriogenology (2000) 53, 1365-1373.Take home message: there is competition between sperm!

What controls testicular size/ sperm production?

Each Sertoli cell has a fixed capacity for the number of germ cells that it can support.

Therefore, the number of Sertoli cells in the adult testis determines (testis size) daily sperm production.

Sharpe, Reproduction(2003) 125, 769–784

The distribution profile of Sertoli cell number in a population of men: i.e. it is very variable

Sertoli cell number

Final terminal differentiation – losing ability to divide, but switching on spermatogenic support functionHypothesis:

Disturbances in testicular development will affect male fertility.

Proliferation during fetal and neonatal life

Proliferationperipubertally.

Testis

Spermatozoa

Hypothalamus

Pituitary

FSH LH

++

GnRH+

Testosterone

Negative feedback

Inhibin

The “TEXT BOOK” control of the testis and spermatogenesis

Testis

Spermatozoa

Hypothalamus

Pituitary

FSH LH

++

GnRH+

Testosterone

Suppress FSH/LH

GnRH antagonist?

Increase feedback:Give testosterone

Negative feedback

Observation: The 1st large scale trials in 1990s - highly effective in reducing sperm counts in most men, BUT a small % of men failed to show sufficient suppression of sperm – even when gonadotrophin levels were undetectable.

Observation: The 1st large scale trials in 1990s - highly effective in reducing sperm counts in most men, BUT a small % of men failed to show sufficient suppression of sperm – even when gonadotrophin levels were undetectable.

The difficulty of getting a male contraceptive..

Normal testes

“wild type”

Small testes, but still fertile

But in the FSH “knockout”

Conclusion: FSH is NOT essential for spermatogenesis…

Conclusion: FSH is NOT essential for spermatogenesis…

For many years, FSH had been seen as the main driving force in spermatogenesis…

FSH

Sertoli cells

FSH receptors

Is the same true for man?

Yes - very similar!

Men with an inactivating mutation of the FSH receptor are fertile despite having small testes.

Conclusion:

FSH is not essential for spermatogenesis…

– but does seem to be important in determining testicular size

No Spermatozoa

Hypothalamus

Pituitary

FSH LH

++

GnRH+

Testosterone

Prepubertal boys

Negative feedback

Small testes

Spermatozoa

Hypothalamus

Pituitary

FSH LH

++

GnRH+

Testosterone

Prepubertal boys

Negative feedback

Small testes

Spermatogenesis can Spermatogenesis can occur in testes with occur in testes with Leydig cell tumours in Leydig cell tumours in pre-pubertal pre-pubertal boysboys

Spermatogenesis can Spermatogenesis can occur in testes with occur in testes with Leydig cell tumours in Leydig cell tumours in pre-pubertal pre-pubertal boysboys

Perhaps local Perhaps local steroids may be steroids may be important in important in spermatogenesis?spermatogenesis?

TESTOSTERONE

Perhaps this explains the small % of men who failed to show sufficient suppression of sperm – even when gonadotrophin levels were undetectable – in the contraceptive trials

Perhaps this explains the small % of men who failed to show sufficient suppression of sperm – even when gonadotrophin levels were undetectable – in the contraceptive trials

Intra-Testicular Circulation

T 1500 25 nmol/L

E2 11000 27 pmol/L

Local steroids may be important in Local steroids may be important in spermatogenesis?spermatogenesis?

Are local steroids Are local steroids really important?really important?

Are local steroids Are local steroids really important?really important?

Leydig cellsSertoli cells

Peritubular cells

AR

AR null

AR

AR

Location of androgen receptors

Androgen receptor knockout (AR null)

WT

Direct evidence that testosterone acting via Sertoli cells is important for later stages of spermatogenesis.

Where are the steroids acting?

Where are the steroids acting?

Small testes

AR-null

Leydig cellsSertoli cells

Peritubular cells

Androgen receptor knock-out in Sertoli cells only

AR

AR

AR

Result: Spermatogenesis becomes arrested during meiosis

Testosterone

↑↑ later stages of spermatogenesis

FSH

↑ Leydig cell no.

↑↑ early Sertoli cell proliferation

↑↑ later Sertoli cell proliferation Initiates spermatogenesis↑↑ Spermatogonia no.

LH

AR

AR

Conclusion:

Sequential, coordinated

actions of LH, FSH and

androgens are required.

Conclusion:

Sequential, coordinated

actions of LH, FSH and

androgens are required.

Leydig cell development

Peri-tubular cells

By end of 1st year, few Leydig

cells left

2nd wave of Leydig cells (peaks at 3

mo ) + T surge

1st wave of Leydig cells. T production stimulated by

hCG

Adult Leydig cells differentiate from undifferentiated

precursors

Sertoli cell number

Leydig cells

Men: 100-200 m sperm each day

Men: 100-200 m sperm each day

The no. of sperm determined by no. of Sertoli cells.

The no. of sperm determined by no. of Sertoli cells.

Sperm count (106/ml)

Sperm count (106/ejaculate)

Daily sperm production (106/testis)

% m

en

% b

ecom

ing

pre

gnan

t p

er c

ycle

. Sertoli cell number/testis (m)

FertilityFertility

The number of Sertoli cells is fixed by puberty.

Largely determined by rate of proliferation in fetus and 1-9 months post-natal.

The number of Sertoli cells is fixed by puberty.

Largely determined by rate of proliferation in fetus and 1-9 months post-natal.

Therefore, factors affecting no. of Sertoli cells in early life will

influence sperm counts in adulthood.

Therefore, factors affecting no. of Sertoli cells in early life will

influence sperm counts in adulthood.

The sperm count in men varies. Normally, 100-200 m sperm each day

The sperm count in men varies. Normally, 100-200 m sperm each day

If sperm count is too low, fertility

declines

If sperm count is too low, fertility

declines

FSH Testosterone from fetal Leydig cells

Endocrine disrupting compounds