Ovarian follicular and luteal dynamics

Question 1

Theories of follicular dynamics

Answer 1

1. Continuous
2. Wave pattern

Question 2

Continuous

Answer 2

-follicular growth and regression is continuous process and is independent of the phase of reproductive cycle

Question 3

Wave pattern

Answer 3

A reservoir of antral follicles remains in a resting stage and at a certain time in each species, one or several of the follicles begin to grow and reach maturity during estrus

Question 4

Estrous

Answer 4

duration between heats

Question 5

Bovine estrous cycle follicle development

Answer 5

-uses wave pattern of follicles
-more than 95% of bovine estrous cycles are composed of 2-3 follicular waves

Question 6

Stages of follicle development

Answer 6

1.Recruitment
2. Selection
3. Dominance
4. Atresia

Question 7

GnRH release

Answer 7

1. tonic and surge centers in hypothalamus control release of GnRH
   >Tonic: spontaneously; rhythmic fashion
   >Surge: only activated with estradiol (estrogen from growing antral follicles) AND low progesterone!
2. Follicles and their growth depends on the amounts of FSH and LH

Question 8

Recruitment

Answer 8

-The phase of follicular development in which a group of small antral follicles begins to grow
>occurs based on surge of plasma FSH concentrations

-when follicles within the wave get larger, produce more and more estradiol which provides negative feedback to hypothalamus to stop production of GnRH and therefore FSH because these follicles are growing and don’t need more!

Question 9

Selection of follicles

Answer 9

-Follicles are selected from previously recruited small follicles and either become atretic or develop further
>follicles shift their dependence from FSH to LH

Question 10

Dominance

Answer 10

The dominant follicle in the wave is defined as the one that reaches the largest diameter

Question 11

Atresia

Answer 11

degeneration of antral follicles

Question 12

How does the dominant follicle become dominant?

Answer 12

1.Surge results in release of FSH starting follicular wave
2. After surge, FSH declines and the growth of most follicles will stop and they will begin to regress within 2-5 days
3. This does not stop the dominant follicle which reached the threshold and switched from FSH dependent to LH dependent

Question 13

Ovulation of dominant follicles

Answer 13

-dominant follicle increases amounts of estradiol production causing a positive feedback to the pituitary, and when estrogen threshold met= surge of LH (10x amount of tonic level)

=RESULTS in ovulation a day later

Question 14

Anovulatory vs ovulatory wave estradiol concentrations

Answer 14

Anovulatory- less estradiol present

Ovulatory- more estradiol production (2x as much)

Question 15

Development of corpus luteum after ovulation

Answer 15

-At time of ovulation, antral contents are evacuated and the wall of ovulatory follicle collapses into undulations within the vacated antrum = CL

Question 16

What does CL produce?

Answer 16

CL produces progesterone

Question 17

Role of progesterone

Answer 17

-correlated to CL weight and volume

-Will block the surge center by blocking GnRH production by hypothalamus and the production of LH and FSH by pituitary

Question 18

Follicular dynamics in a pregnant cow

Answer 18

• Endogenous progesterone is produced from the CL
  1. regular emergence of anovulatory follicular waves (except last 21 days)
  2. Dose-related suppression of LH and dominant follicle growth
  3. Max follicular diameter and intra-wave intervals decrease

Question 19

Luteolysis

Answer 19

-occurs when pregnancy not present
-breakdown by prostaglandin F2alpha released by endometrium around days 17-19 in cows estrous cycle

Question 20

Prostaglandin F2alpha release in non-pregnant cows

Answer 20

-occurs at days 17-19

Question 21

What does luteal cell death cause?

Answer 21

-causes a drop in progesterone due to vascular supply disruption, release of cytokines, and infiltration of macrophages

Question 22

Routes of PGF2alpha

Answer 22

1. systemic (mare)
2. Local (ruminants)
3. Both local and systemic (pigs and camelids)
4. progesterone similar in pregnant and non pregnant dogs (~60 days post LH surge). Pregnant: progesterone drops suddenly, non-pregnant: progesterone drops slowly

Question 23

Follicular dynamics in prepubertal calves

Answer 23

Anovulatory follicular waves regular pattern
1. FSH surges are coupled to wave emergence
2. follicle dominance increases with age
3. max follicular diameter and interwave follicle increase with age
4. circulating LH increases with age

Question 24

Prepubertal calves first ovulatory cycle

Answer 24

-8 days
-short lived, under developed CL
- 1 follicular wave

Question 25

Ovulation hormone summary

Answer 25

1.FSH starts follicular wave
2. Progesterone high from CL= no LH peak= no ovulation
OR
progesterone low from no CL then estrodiol from dominant follicle causes positive feedback to anterior pituitary for LH surge
3. LH surge releases oocytes from the dominant follicles= OVULATION

Question 26

What do ovulation tests look for?

Answer 26

High levels of LH because LH surge means that ovulation occurred

Question 27

Two-wave vs three wave cycles

Answer 27

-more than 95% of cycles
-does not effect preg. rates

Differences:
1.duration of cycle (19-20 vs 22-23 days)
2. Interwave interval (10 vs 8 days)
3. Max size of 2nd dominant follicle (15-13mm)
4. Onset of luteolysis (day 16 vs 18)

Question 28

Initiation of follicular dominance

Answer 28

-size advantage of the dominant follicle from the time of emergence
-hierarchical progression over rest of FSH surge= dominant follicle emerged 6-12 hrs earlier than other follicles
-wave emergence at 1mm (2.5 days earlier than previously known)
-High FSH sensitivity (within 6hrs)

Question 29

Reproductive senescence

Answer 29

Refers to the gradual decline in reproductive capacity with age

Question 30

What factors play a role in reproductive senescence?

Answer 30

-continued 2 or 3 wave patterns; most mother-daughter pairs has the same pattern
-elevated FSH
-interovulatory and interwave intervals did not change
-CL smaller, progesterone lower
-fewer follicles at emergence
-lower super stimulatory response
-lower fertilization rate