Effects of Nutrition on the Estrous Cycle

Question 1

What are the two nutritional states that can affect the estrous cycle?

Answer 1

under nutrition

increased nutrition

Question 2

What does short term severe under nutrition cause?

Answer 2

almost immediate decrease in GnRH and LH levels

rapidly reversed when normal nutrition is restored

Question 3

What does long term malnourishment cause?

Answer 3

decrease in GnRH and LH levels

starting them on normal ration will not always reverse

Question 4

Critical body fat hypothesis

Answer 4

a certain degree of fatness is necessary for normal reproduction

(12-14% for males, 22% for females)

Question 5

Metabolic fuels hypothesis

Answer 5

acute changes in caloric availability can control GnRH secretion

Question 6

What is leptin?

Answer 6

• peptide hormone secreted from white adipose tissue

- circulating levels are directly correlated with fat stores

Question 7

How does leptin function as a permissive signal for pulsatiile secretory activity of GnRH neurons?

Answer 7

leptin inhibits NPY neurons that are in turn inhibitory on GnRH neurons

(by inhibiting the inhibitor, it allows GnRH secretion)

Question 8

What happens when fat stores decline (in regards to leptin)?

Answer 8

circulating levels of leptin drop and the GnRH pulse generator is suppressed

Question 9

What is ghrelin?

Answer 9

peptide hormone secreted by the stomach in an endocrine manner

(secretion increases with fasting, so it is a signal of energy insufficiency)

Question 10

How does ghrelin function to suppress GnRH?

Answer 10

recent evidence suggests it suppresses the kisspeptin system and thus suppresses GnRH

Question 11

What is insulin-like growth factor 1 (IGF-1)?

Answer 11

produced by the liver in response to growth hormone stimulation

Question 12

How does IGF-1 function to increase GnRH?

Answer 12

can directly enhance secretion in GnRH neurons and can act indirectly by increasing kisspeptin secretion from KND neurons

Question 13

What are the 2 parts of the metabolic fuels hypothesis

Answer 13

1. the fuel has to be present in the body in sufficient quantitiy
2. the fuel has to be available for oxidation in tissues

Question 14

What is the most important fuel that the body is detecting?

Answer 14

glucose

Question 15

What site detects the information about metabolic fuel oxidation?

Answer 15

area postrema (AP) located in the hindbrain

Question 16

How does information from the hindbrain influence GnRH neurons?

Answer 16

• neuronal projections from the hindbrain inhibit GnRH neurons directly using neuropeptide Y (NPY) and catecholamines
• NPY and catecholamine neurons from the hindbrain activate CRH neurons which then inhibit GnRH neurons

Question 17

What do insulin and IGFs together promote?

Answer 17

granulosa cell proliferation and steroidogenesis

Question 18

Falling IGF-1 during under nutrition results in what?

Answer 18

it has a potentially direct ovarian role in reducing cyclicity

Question 19

What does an increase in nutrition results in?

Answer 19

results in an increase in the number of mature follicles that develop per cycle and thus the number of ovulations and eventually in increased litter size

Question 20

Name and describe the 3 nutritional effects

Answer 20

1. Acute effect - seen before bodyweight change is detectable
2. Dynamic effect - seen while bodyweight is increasing
3. Static effect - seen when body weight is maintained at high levels

Question 21

What happens when glucose and insulin are increased?

Answer 21

• increased glucose uptake into follicles

- suppresses estradiol secretion from follicles

Question 22

What happens when leptin is increased?

Answer 22

suppresses estradiol secretion from follicles

Question 23

What happens when intrafollicular IGFBP is increased?

Answer 23

suppresses estradiol secretion from follicles

Question 24

Suppression of estradiol secretion from follicles results in what?

Answer 24

less feedback inhibition of FSH secretion so more follicles are supported through the selection process

Question 25

What is flushing?

Answer 25

females are put on a high plane of nutrition 2-3 weeks prior to breeding (only works in undernourished ewes and only brings them up to the reproductive level of normally conditioned animals)

Question 26

What are sodium ionophores and why would you use them?

Answer 26

alters rumen microflora to have propionate as the product of fermentation, which increases insulin and increases pituitary sensitivity to GnRH (improved reproductive performance)

Question 27

Why would you increase dietary fat?

Answer 27

results in increased propionate production and therefore improved reproductive performance

Question 28

Why would you increase n-3 unsaturated fats?

Answer 28

can reduce the formation of prostaglandin by the uterine endometrium and decrease the sensitivity of the CL to prostaglandins that are released (longer estrous cycle and increased embryo survival)

Question 29

Low protein diets cause what?

Answer 29

cessation of estrous cycles in monogastrics

Question 30

High protein diets cause what?

Answer 30

decrease oocyte quality with reductions in fertilization rates and blastocyst formation

Question 31

Stress effects on breeding

Answer 31

- reduction in GnRH and LH following transport stress - high cortisol and low sex steroid levels are not reproductively successful - a change in an individual's social status can also be stressful

Question 32

Stress effects on gestation

Answer 32

-crowing causes social stress which leads to immunocompromised animals

Question 33

What are the effects of stress on tonic GnRH secretion?

Answer 33

- stressful situations cause release of CRH and arginine vasopressin (AVP) in the hypothalamus - CRH and AVP interact with inhibitory interneurons that affect activation of GnRH neurons

Question 34

What are the effects of stress on generation of the LH surge?

Answer 34

-acute stress reduces GnRH secretion from the hypothalamus and no GnRH means no LH secretion

Question 35

When would an animal override the inhibition of stress?

Answer 35

1. old individuals that have little chance of future reproductive success 2. seasonal breeders, especially very short breeding seasons 3. species where both partners provide parental care 4. semelparous species where there is only one breeding period followed by death 5. dominant animals in social groups where only the dominant pair breed and dominance is temporary