The Hormones of Reproduction:

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Chapter 4

• The Hormones of Reproduction
• Gonadal Hormones

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Gonadal Hormones
What are gonadal hormones? Hormone- Substances
produced by a specialized group of
cells that are transported in the blood or
lymph to modify some genetically-condi- tion
ed end organ. Gonadal Hormone- Hormonal
substance produced by the gonads( Testes
Ovaries)
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How are they different from gonadotropins? 1.
Site of secretion 2. Chemical structure 3.
Target tissues
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Gonadal Hormones
Testes- Androgens Ovaries- Estrogens
Progestogens Relaxin Activin Protein
hormones Inhibin
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Gonadal Steroids

• Misnamed because they can also be produced by the
  adrenal cortex and the placenta of many species.

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Classes

• Androgens- male sex steroid i.e., Testosterone
• -produced by males and females
• Estrogens- female sex steroid, i.e.,
• Estradiol (E2)
• -present in both male and female
• Progestogens- they are progestational or
  pregnancy protecting, i.e., Progesterone (P4)

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Gonadotropin Receptor stimulates production of
cAMP which triggers formation of protein
kinase-- Protein kinase
Cholesterol Testosterone Estradiol
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Steroid synthesis

• All steroids are derived from cholesterol via an
  intermediate compound (pregnenolone)-

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Steroid Synthesis
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Male Hormones
Androgens Testosterone 5? androstenone - Boar
taint 16 androstenes - pheromones (saliva and
sweat) Control of Secretion GnRH?LH ? leydig
cells ? androgens Diagram (hypothalamus-pituitary
-testes)
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Functions of Androgens 1. Stimulate
spermatogenesis 2. Stimulate the secondary sex
organs to grow, develop, and become
secretory 3. Maintain the life span of the
epididymal sperm 4. Stimulate secretory
activity of the accessory sex organs 5.
Stimulate libido(sexual desire) 6. Stimulate
nitrogen retention for muscle formation
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GnRH
Body Tissues
Sex Organs
Testosterone
Testes
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Uses

• Injection to develop teaser animals for estrous
  detection purposes
• Growth promotants e.g., Synovex-S
• Stimulate muscle mass- Steroid use in
  professional athletes

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Male Hormones

• Terms
• Cryptorchids
• Proud Cut
• Ridgling
• Stag

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Estrogens -Types of estrogen -Site of
production -When is it produced? -What controls
its production? -Two cell - two gonadotropin
theory theca interna LH granulosa
cells FSH -How is GnRH involved? - Diagram
control of reproductive hormones?
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Female Steroids Estradiol Estrogens
Estrone Estriol

• Heat
• Uterine motility
• 2. Glandular duct growth in uterus (endometrium)
• 3. Histological changes in vaginal epithelium
• 4. Duct growth in mammary glands
• 5. Carcinogenic
• 6. Control the release of pituitary hormones

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What does Estrogen do?
1. Stimulate the occurrence of female sexual
receptivity (libido) Estrogen also
stimulates lordosis 2. Stimulate the growth and
development of the uterine
endometrium tissue growth- rapid
mitosis Estrogen increases the mass of the
endometrium and myometrium
(cell hyperplasia and hypertrophy)
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• 3. Acts on uterus to increase both amplitude and
  frequency of contractions by potentiating the
  effects of oxytocin and PGF2 ?
• 4. Increase blood flow to the vagina and vulva
• 5. Stimulates duct growth and causes development
  of the mammary gland

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• 6. Increases water retention of the vulva,vagina,
  
• and uterus
• 7. Increases retention of Na, Cl-,
• and promotes fat deposition
• 8. Development of female sex
• characteristics is due to Estrogen
• 9. Estrogens have both negative and
• positive control through the hypothalamus

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• 10. Estrogens have been used as abortifactents
• A. Luteolytic action
• B. Luteotropic in the sow ( Day 11-16)
• 11. Non-reproductive effects
• A. Uptake of calcium
• B. Maturation of epiphyseal groove

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Behavioral effects

• Progesterone acts synergistically with E2
  inducing behavioral estrus in ewe and cow
• Estrogens Wide range of physiological effects
• Positive and Negative feedback ? Hypothalamus
  LH and FSH
• Negative- tonic center
• Positive- preovulatory center

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Function of Estrogens

• Stimulate Tissue Growth
• Increase uterine contractions
• swelling

• -Increase the mass of both the endometrium and
  myometrium cell growth
• -cell division
• -increase both frequency and amplitude of uterine
  contractions
• -increase blood flow to vulva and vagina

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Functions of Estrogens

• Stimulate duct growth within the mammary gland

• - water retention

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Review

• Estrogens
• Estradiol released from granulosa cells
• Estrone released by placenta
• Estriol conversion product of the other two
• Function of estrogens
• 1. Stimulate the manifestation of estrus
• 2. Stimulate cyclic changes in the female
  tract
• a. H2O content - ? E2 ? H2O to protect tissue
• b. Mucus production

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ReviewFunction

• 3. Stimulates cellular changes
• a. increases layers of cells in female tract
• -Hyperplasia - ? cell no.
• -Hypertrophy- ? cell size
• 4. Stimulates mitosis
• a. carcinogenic - cervical cancer
• - prostate cancer
• - sertoli cell cancer
• - breast cancer

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ReviewFunction

• 5. Increases duct development
• a. Endometrium
• b. Mammary gland
• 6. Effect on secondary sex characteristics
• a. Length of long bones
• closure of epiphiseal groove
• b. Ca uptake

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• Progestogens- compound having a progestational
  effect
• -secreted by luteal cells of the C.L. also by
  the placenta and adrenal gland

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What does Progesterone do?
Pro- Favor gesterone- gestation 1. Determines
length of cycle 2. Causes development of
secretory endometrium of uterus. 3. Slows
down contractions of the uterus. 4. Produced by
CL throughout the cycle or pregnancy if pregnant.
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Estrous Cycle

• Healthy, non-pregnant cows undergo regular
  repetitious cycle of events
• Typically every 21 days (range of 18-24 days)
• Measured by interval to next estrus (heat)
• Estrus (heat)
• Period female is sexually receptive to male
• Precedes ovulation (release of egg for
  fertilization)
• Repeated opportunities for pregnancy

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Estrous Cycle

• Produces hormone progesterone
• Hormone of pregnancy
• Prepares uterus and maintains pregnancy

estrus
P4
1 3 6 9
12 15 18
21
Day of estrous cycle
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Estrous Cycle

• If pregnancy not detected by day 15
• Uterus produces prostaglandin F2?
• Absence of an embryo
• Transported to ovary

estrus
P4
PGF2?
1 3 6 9
12 15 18
21
Day of estrous cycle
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Estrous Cycle

• If pregnancy not detected by day 15
• Corpus Luteum (CL) regresses
• Progesterone production decreases

estrus
P4
PGF2?
1 3 6 9
12 15 18
21
Day of estrous cycle
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Estrous Cycle

• Follicular waves
• Generally range in length from 7-12 days
• Usually 2 or 3 waves during a single estrous cycle

estrus
estrus
1 3 6 9
12 15 18
21
Day of estrous cycle
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• Smooth Muscle Control
• -Inhibits the motility of the myometrium
• -Slows down contractions of the uterus

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• Function
• Tissue Differentiation
• -Prepare the uterus for implantation and
  maintenance of pregnancy by increasing secretory
  glands in the endometrium
• - Develops secretory tissue (alveoli) of the
  mammary gland
• Determines length of the cycle
• -Maintenance or regression of C.L.
• -If fertilization takes place the life of the
  C.L. is prolonged thus more production of P4?
  inhibiting LH surge
• -If fertilization does not take place uterine
  secretions cause the demise of the C.L.
  (luteolysis)

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• Behavior Effects
• -Progesterone acts synergistically with E2
  inducing behavioral estrus in ewe and cow
• - Inhibition of sexual behavior sow
• -P4 interferes with production of GnRH thus
  prevents preovulatory surge of LH
• -ie. Determines length of cycle

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Application

• -Progestogens are given to prevent abortion in
  female prone to abortion- explain
• -Due to sufficient progesterone production
• -Most common use- birth control pills?prevent LH
  surge and subsequent ovulation

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• In cattle, synthetic progestogen (norgestomet)
  used to synchronize the estrous cycle in cows
• - Synchromate B E2- P4 implant 9 days
• - Melengesterol acetate (MGA)
• - Increase gains in feedlot heifers
• ?LH surge- allows E2 prod ? ?GH release
  promotes N retention- ? feed efficiency

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Pregnancy Hormones

• Estrogens-
• Produced by early conceptus
• Maternal Recognition
• Produced late in pregnancy (placenta)
• Trigger Parturition
• Progestogens-
• Produced by CL
• Initiate pregnancy
• Produced by placenta
• Inhibit myometrial contractions

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Hormone Sequence Recap
Cyclic Changes during the Estrous
Cycle
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Hormonal Interactions
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Gonadotropin Stimulation of Gonadal Hormone
Production
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Hormone Action at the Cellular Level
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ADENYL CYCLASE
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Steroid Synthesis
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Hormone Structures
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Protein Hormones produced by the Ovary
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• Relaxin- polypeptide hormone 5700 Daltons
• Released only during pregnancy
• Produced by CL
• Produced by placenta and uterus
• Actions of Relaxin
• Dilation of cervix and vagina before parturition
• Inhibits uterine contractions
• Causes increased growth of mammary glands
• Separation of pubic symphysis within 6 hours of
  injection

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Activin

• Gonadal glycoprotein
• Protect FSH releasing dimer
• Purified from gonadal fluids
• Autocrine and paracrine modulator of production
  of steroids and other hormones
• Substance believed to be produced by the ovary
• Known to stimulate release of FSH from pituitary
• cells in culture media
• Never shown to be functional in vivo

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Inhibin

• Protein Hormone
• Produced by granulosa cells of the follicle
• Role
• -Controls the release of FSH
• -Dominant Follicle Theory
• -Controls Ovulation Rate- Pig, Ewe

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