Physiology and Endocrinology in the Male

Question 1

Develop understanding of Seasonal regulation in short and long day
breeders

Answer 1

• Horses are Long daylight breeders (GestaEon ~ 340 days Designed to Foal during spring/summer)
• Goats and Sheep are short daylight breeders (GestaEon ~ 150 days designed to kid/lamb in spring/summer)

Melatonin production is decreased with increased light
* Peak melatonin production during winter

Melatonin has negative effect on GnRH release in the stallion (long day breeder)
* Melatonin has positive effect on GnRH release in the Ram or Buck (short day breeders)
* Kisspeptin

• Opioids may mediate seasonal activity as well.
  (opioid antagonist can cause LH surge in Stallion outside of breeding season)

“Specula)on that seasonality is regulated by rela)ve ac)vity of
Kisspep)n and RFRP3.”

Question 2

What are the glycoprotein hormones?

Answer 2

Glycoprotein Hormones:
* Large molecules with protein subunits
* Typically have receptors within cell
membrane
* oIen cause enzyme ac3va3on
* LH, FSH, TSH

Question 3

What are the neuropeptides?

Answer 3

Neuropep4des: Small chain amino acids
secreted by neurons or neurosecretory cells
* Kisspep3n, Oxytocin, Prolac3n

Question 4

What are the steroid hormones?

Answer 4

Steroid Hormones
* Smaller molecules
* Cholesterol Based
* May migrate across cell membrane
and nucleus
* Target DNA, ini4ate mRNA synthesis
* Testosterone, Estradiol, Proges3ns

Cells will have receptors for all hormones and enzymes regardless of the
animal’s gender

• Receptor expression may be influenced by certain hormones or other
  environmental factors
• Receptor upregulation, changes in affinity etc.

Question 5

What are the 3 centers of the sexually dimorphic Nucleus of the hypothalamus and the feedback modalities?

Answer 5

Male has Three functional regions within the SDN with variable hormone receptors:

1.) Libido Testosterone > (Aromatase) > Estradiol + Behavioral Libido
2.) Male Aggression Testosterone= Male Aggression
3.) Pulse Generator > Releases Kisspeptin
Has Estrogen, Testosterone and Progesterone receptors (-Feedback)

Question 6

What is the role of estradiol?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 6

Conversion of Testosterone at Libido center in SDN

• Conversion of Testosterone to Estrogens in Sertoli cells
• Modulation of Spermatogenesis

feedback at H-P axis

• Sperm maturation in epididymis (reabsorption of seminiferous tubule fluid)

Question 7

What is the role of LH?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 7

• From Anterior Pituitary, primary role is testosterone production by Leydig
  cells
• LH receptors in Leydig cellsà through Enzyme activation à Convert
  cholesterol into Pregnenolone
• LH affects regulation of StAR protein which is needed for cholesterol
  transport into cell
• LH affect on Leydig cell is modulated by other substances such as Growth
  Hormone, Insulin-like Growth factor-1 , and others

Question 8

What is the role of FSH?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 8

• From Anterior Pituitary, acts on Sertoli cells for Androgen Biding Protein(ABP)
  synthesis, Conversion of testosterone to estrogens, secrete Inhibin and ac3vin
• ABPà Testosterone in Sertoli cellsà protein synthesis to support spermatogenesis
• Testosteroneà(Aromatase)à Estrogens
• Inhibin and Ac3vin feedback to H-P axis.

Question 9

What is the role of testosterone?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 9

• From Testes, predominant role is for spermatogenesis, matura3on in
  epididymis, accessory sex gland func3on, secondary male sex characteris3cs
• Testosterone à(5 Alpha reductase)à DHT

Testosteroneà prostate that contains 5 alpha reductaseà DHTà ProstaDc fluid

• Testosteroneà(Aromatase)à Estradiol (Libido center at SDN)

Question 10

What is the role of inhibin?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 10

• From Sertoli cells
• Negative feedback on FSH secretion at Pituitary
• Paracrine àLeydig cells for steroidogenesis
• Paracrineà spermatogenesis

Question 11

What is the role of activin?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 11

• From Sertoli cells
• Suspect + feedback on FSH secre3on at pituitary

Question 12

What is the role of thyroid hormone?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 12

• Important for Leydig and Sertoli cell
  differen5a5on/matura5on
• StAR mRNA is important for transport of cholesterol
  across cell membranes and testosterone produc5on. Low
  Thryoid hormone levels will decrease the amount of StAR
  mRNA and Testosterone
• Thyroid hormone is involved in Sertoli cell produc5on of
  AMH, Aromatase and And Estradiol receptors, and
  Androgen binding proteins. (Juan Samper 2009)

Question 13

What is the role of growth hormone?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 13

• Mediates release of LH
• Produc5on of IGF-1 From Tes5s
• May effect sperm mo5lity
• May have ega5ve effect on Testosterone produc5on

Question 14

What is the role of prolactin?

• S3mulus for release of hormones
• loca3on of origin
• target 3ssues
• outcome at target 3ssues
• Feedback regula3ons

Answer 14

• From Anterior Pituitary (Lactotrophs)
• Induce Estrogen receptors
• Promote Spermatogenesis

Synthesis of LH receptors in testes (in conjunction with LH and GH)
Activate androgen synthesis

• Dopaminergic modulators affect secretion