Lecture 3

Question 1

What are the general characteristics of follicular waves?

Answer 1

-cows and mares have wave-like patterns of follicle growth, development, and regression
-maturation and ovulation does not occur unless an LH surge occurs
-normal cyclic pattern of estrus activity will not occur until animal is capable of generating an LH surge
-cows have 2 to 3 wave estrous cycles; mares have 1 to 2
-new waves emerge around mid-luteal stage

Question 2

Why is it important that inhibin and estradiol decrease after ovulation?

Answer 2

it allows for FSH production to start up again and for the cycle to restart

Question 3

When can an LH surge occur?

Answer 3

after luteolysis of the corpus luteum

Question 4

When does the first wave of a new estrous cycle emerge and why?

Answer 4

around 3 to 4 days after an LH surge, because there is an accompanying rise in FSH secretion

Question 5

What prevents dominant follicles from early waves from maturing?

Answer 5

presence of the corpus luteum; CL must regress to allow for LH surge and further follicle maturation

Question 6

Which hormone establishes the cyclic pattern of reproductive behavior?

Answer 6

progesterone

Question 7

What causes luteolysis to occur?

Answer 7

secretion of prostaglandin F2a from the epithelial cells of uterine endometrium IF they do not receive a signal from a viable conceptus

Question 8

In which species is prostaglandin the cause of luteolysis?

Answer 8

-mare
-cow
-ewe
-doe
-sow
-llama

Question 9

How does luteolysis occur in bitches and queens?

Answer 9

bitch: withdrawal of prolactin leads to decline in plasma P4 at end of pseudopregnancy
queen: unknown mechanism for decline in P4

Question 10

How does the ovary of the mare differ from other species?

Answer 10

-medulla is on the outside and cortex is on the inside
-CL forms on the inside with the cortex; it cannot be felt on palpation like in cows

Question 11

What are the characteristics of the queen’s repro cycle?

Answer 11

-no pregnancy or pseudopregnancy is followed by inter-estrous period of 2 to 3 weeks once the follicles undergo atresia
-cats in the house exposed to longer light hours may become non-seasonal
-melatonin effects are similar to those in mares

Question 12

How does the preovulatory LH surge trigger ovulation?

Answer 12

-increases blood flow to ovary and dominant follicle, causing edema and increasing follicular pressure
-increased PGF2a leads to increased contraction of ovarian smooth muscle and increased follicular pressure
-increased PGF2a leads to release of lysosomal enzymes that weaken follicular wall
-shift from E2 to P4 by dominant follicle increases P4 and collagenase to weaken follicular wall

Question 13

How does the preovulatory LH surge contribute to fertilization?

Answer 13

by allowing for gap junction breakdown between the granulosa cells and oocyte

Question 14

How do large and small luteal cells differ?

Answer 14

-small luteal cells maintain prostaglandin receptors
-large luteal cells come from granulosa cells and produce majority of oxytocin

Question 15

What changes allow for the uterus to produce oxytocin?

Answer 15

-PGF is synthesized in the endometrial epithelial cells after about day 10 of the luteal phase
-inhibition of oxytocin receptors due to high P4 levels is lost around day 10-12 of the luteal phase

Question 16

What is the role of large luteal cells?

Answer 16

synthesize and store oxytocin

Question 17

How do oxytocin and PGF act on the CL in the absence of pregnancy?

Answer 17

-oxytocin from the CL binds to uterine receptor to stimulate PGF release
-PGF acts on the CL to stimulate another release of oxytocin
-cycle continues; amplitude and frequency of PGF release increases until CL is destroyed

Question 18

Where is prostaglandin metabolized?

Answer 18

the lungs

Question 19

Which embryonic structure forms the uterine horns?

Answer 19

paramesonephric ducts

Question 20

What are the pregnancy recognition factors in each species?

Answer 20

-bitch: none needed
-cow: bTP-1
-ewe: oTP-1
-mare: 3 proteins/estrogens (still unknown)
-queen: none needed
-sow: estradiol/E2
-human: hCG

Question 21

What are the pathways by which PGF is delivered to the CL?

Answer 21

-systemic pathway in the mare
-local countercurrent exchange from ipsilateral uterine vein to ovarian artery in ruminants
-both in the sow

Question 22

Why do ruminants rely on the countercurrent exchange to deliver PGF to the CL?

Answer 22

-98% of a cow’s prostaglandin is metabolized in the lung compared to a mare’s 40-60% and sow’s 20-40%
-this leaves only 2% of prostaglandin to go into circulation and reach the CL, which is not enough to cause luteolysis

Question 23

How does the embryo impact maternal recognition of pregnancy in the cow?

Answer 23

embryo elongates to the non-pregnant horn to stop this horn from continuing to produce prostaglandin

Question 24

How does the embryo impact maternal recognition of pregnancy in the mare?

Answer 24

embryo moves throughout uterus and both horns to achieve recognition and stop prostaglandin production

Question 25

Why is it important that the two uterine horns do not have a cross-over in blood supply?

Answer 25

products produced by one horn will not affect the other

Question 26

Which ovary typically undergoes follicle development and ovulation in cows?

Answer 26

right ovary (no pressure/issues due to rumen on this side)

Question 27

What happens if a cow has a partial uterectomy of the left horn, contralateral to the CL?

Answer 27

-cow can go through the estrous cycle again -the horn can produce prostaglandin to lyse the CL

Question 28

What happens if a cow has a partial uterectomy of the right horn, ipsilateral to CL?

Answer 28

CL persists; no prostaglandin production occurs to cause luteolysis

Question 29

What are the 3 ways to fix a partial uterectomy of the right horn, ipsilateral to CL?

Answer 29

-external prostaglandin administration -removal of ovary with the CL -cull the cow (most practical and most chosen option)

Question 30

What happens when a cow has a total uterectomy/no uterine horns?

Answer 30

-no prostaglandin production to cause luteolysis; CL persists -must cull cow