13 - Male Endocrinology and Puberty

Question 1

Source, target and action of GnRH in males

Answer 1

Source: hypothalamus
Target: gonadotroph cells (anterior pituitary)
Action: release FSH and LH

Question 2

FSH source, target and action in males

Answer 2

Source: gonadotroph cells (anterior pituitary)

Target: sertoli cells (testes)

Action:
- maintain spermatogenesis
- stimulate androgen binding protein (ABP) production

Question 3

Source, target and action of LH in males

Answer 3

Source: gonadotroph cells (anterior pit)

Target: leydig cells (testes)

Action: testosterone production

Leydig cells equivalent to theca interna cells

Question 4

Source, target of T4 in males

Answer 4

Source: leydig cells (testis)

Target:
- hypothalamus/ brain
- reproductive tract
- muscle

Question 5

Action of T4 in males

Answer 5

Male sexuality:
- increase sexual beh and characteristics
- decrease GnRH production
- increase spermatogenesis
- increase muscle development
- accessory sex glands

Question 6

Source, target and action of androgen binding protein

Answer 6

Source: sertoli cells (testes)

Target: N/A

Action: binds T4 in seminiferous tubules to stimulate spermatogenesis

Question 7

Source, target and action of inhibin in males

Answer 7

Source: sertoli cells (testis)

Target: gonadotroph cells (anterior pit)

Action: inhibit FSH secretion

Question 8

Slides 8,9

Answer 8

Positive and negative feedback
Hypothalamic-hypophyseal testicular axis

Question 9

Large concentrations of T4 do what?

Answer 9

Reduce spermatogenesis and fertility

Question 10

How does GnRH discharge work in males

Answer 10

No surge center
Discharged in frequent pulses or bursts
Pulses last for a few moment and occur several times a day

Question 11

How does LH, FSH and testosterone surge work

Answer 11

LH and FSH surges induced by GnRH pulses
Testosterone surges induced by LH (continued stimulation for spermatogenesis)

Question 12

Slides 11,12,13

Answer 12

GnRH, LH, FSH surge
T4 and LH
Steroid secretion patterns

Question 13

What is puberty

Answer 13

Process of acquiring reproductive competence

Question 14

Characteristics of pubescent process in the male

Answer 14

• behavioural traits are expressed
• ejaculation ability
• spermatozoa present in ejaculate
• adequate sperm production to accomplish fertilization

Question 15

What is the limiting factor of the onset of puberty in males? How

Answer 15

Hypothalamus
Onset of puberty requires secretion of GnRH at frequency and quantities appropriate to stimulate gonadotropin (FSH and LH) release by anterior pituitary a levels adequate to support gametogenesis

Question 16

In the male, onset of puberty occurs due to…

Answer 16

Decreased hypothalamic sensitivity to negative feedback of testosterone

Question 17

Five endocrine steps leading to puberty in the male

Answer 17

1. Increase in GnRH pulse amplitude/ freq = increase in LH and FSH
2. Leydig and sertoli cells mature, T4 remains basal
3. When T4 production increases, LH and FSH decrease due to negative feedback on hypo
4. T4 continues to increase from leydig cells in response to LH
5. T4 builds to adult levels (so does GnRH pulses)

Slide 17

Question 18

Slides 18,19

Answer 18

Figures

Question 19

Puberty age range in cattle, sheep, horses, dogs, cats, swine

Answer 19

Cattle: 7-18 months
Sheep: 6-9 months
Swine: 3-8 months
Horses: 13-18 months
Dogs: 5-12 months
Cats: 8-10 months

Question 20

Factors affecting onset of puberty in males

Answer 20

• plane of nutrition
• rate of growth
• exposure to environmental cues
• genetic background

Question 21

Slide 22

Answer 21

Metabolic signals on GnRH

Question 22

What environmental conditions affect puberty in males?

Answer 22

• photoperiod (seasonal breeders: sheep, goats, horses): T4 levels and testes size varies with season
• social contact (male-female, male-male)

Question 23

Slides 24, 25

Answer 23

Testicular size and T4 concentrations in male polar bears

Question 24

Why is early onset of puberty in males important?

Answer 24

Reduce generation interval and advance genetic improvement
- genetically superior males produce semen earlier/longer
- limit “down-time” waiting for onset of puberty