92.Hormonal effects in the ovary; hormones of the ovary

Question 1

Hormones modulating the ovarian functions

Answer 1

• FSH
• LH
• PGF2α

Question 2

Hormones produced by the ovary

Answer 2

• Estrogens
• Progesterone
• Inhibin
• Relaxin

Question 3

Follicle-stimulating hormone (FSH)

Answer 3

-Peptide hormone (2 subunits – α and β)
-Half time: 2 hours
Secretion is regulated by:
• GnRH
• Sexual steroids (Estrogen, Progesterone) • Inhibin
Role:
• Follicle maturation
• Stimulates estrogen synthesis in the ovaries

Question 4

Luteinizing hormone (LH)

Answer 4

Peptide hormone (2 subunits – α and β)
-Half time: 0.5 hours
Secretion is regulated by: • GnRH
• Sexual steroids (positive: E2; negative: P4)
Role:
• Surge center → GnRH↑ → LH peak → Ovulation, luteinization
• Induced ovulators: copulation → neuroendocrine
reflex arch → LH peak → Ovulation, luteinization

Question 5

PGF2α

Answer 5

• PGF2α production in the non-pregnant uterus leads to the lysis of the CL, and consequently to a sharp drop in plasma P4
  -In normal cycle, if the animal is not pregnant, endometrium releases PGF2α on day 16-17 (sheep 13-14) after ovulation.
  • Oxytocin increases PGF2α production
  • Apoptosis of the luteal cells within hours (sharp decrease in
  progesterone level)
  -PGF2α
  • From the endometrium directly to the ovary (Endometrial vein → ovarian artery; Ruminants)
  • Through the systemic circulation (Horse)

Question 6

(O)estrogens

Answer 6

(mostly estradiol – E2)
• Produced in the follicle (2 cells-2 hormones
theory- see later)
• FSH stimulates the production
• Important role in female sexual cycle
-secondary sexual characteristics; ovulation (hormonal feedback mechanisms); endometrial, cervical and vaginal mucosa changes; sexual behaviors, etc.
• Role in non-reproductive functions:
-E.g.: Metabolism, food intake, water homeostasis, protein synthesis, etc.

Question 7

Progesterone (P4)

Answer 7

Produced in the corpus luteum (2 cells-2
hormones theory- see later)
• LH stimulates the production
• Role in female sexual cycle: Implantation and pregnancy
-(Increases the endometrium’s blood supply)
-At the same time progesterone affects the vaginal epithelium and cervical mucus, making it thick and impenetrable to sperm
-inhibits lactation during pregnancy

Question 8

”two cells-two hormones theory”

Early follicular phase

Answer 8

1. In presence of LH, cAMP in theca interna cells increases →
2. Mitochondrial cholesterol uptake increases
3. In mitochondria, pregnenolon is synthetized (precursor of all
   steroid hormones)
4. Pregnenolon is transported to the endoplasmic reticulum (ER)
5. Pregnenolon → progesteron transformation
6. Progsteron → androstendion (male steroid hormone)
   conversion
7. Androstendion diffuses to the granulosa cells through the basal membrane
8. Aromatase enzymes (stimulated by FSH) transforms the androstendion or testosterone (synthetized from the androstendion) to estrone (E1) or estradiol (E2)

Question 9

”two cells-two hormones theory” Early follicular phase

Answer 9

Around ovulation, PRL might inhibit the progesterone – androstenedione conversion
• plasma P4 elevates before ovulation
-In cow, granulosa cells are also able to synthetize pregnenolon

Question 10

”two cells-two hormones theory”

Late follicular phase

Answer 10

In the late follicular phase, E2 production increases (increasing number of FSH receptors – except in mare)
• E2 stimulation: follicular maturation = dominant follicle
- progesterone appears in the circulation.
-Both hormones requires LH and LH receptors for the normal synthesis.
• In the early phase only the cells of theca interna had LH receptors, but later, the granulosa cells express LH receptors (in presence of estrogen and FSH).
• In this phase granulosa cells also produces progesterone trough the same mechanism as the theca interna cells.
- LH is necessary to transform granulosa cells into granulsa-lutein cells (large lutein cells; luteinization).
-Prolactin is able to block the transformation of progesterone in
theca cells.

Question 11

Inhibin

Answer 11

It is produced in the dominant tertiary follicle of the ovary
 Role
• Inhibition of FSH
secretion
Inhibin
• Inhibition of other developing follicles

Question 12

Relaxin

Answer 12

It is produced by the corpus luteum,
– Additional production: breast, placenta and chorion (during pregnancy)
• Role:
– widens the pubic bone and facilitates labor; it also softens the cervix (cervical ripening), and relaxes the uterine musculature.

Question 13

Estrogen effects on the ovaries (summary)

Answer 13

Stimulates follicular maturation
-Increases inhibin and follistatin synthesis
-Increases FSH receptor numbers on the dominant follicle
-Increases LH receptor number on the granulosa cells (LIF mechanism)
-Indirect effect on the ovaries:
• High level of estrogen increases the LH peak (negative-positive feedback shift)