Flashcards in Effects of Nutrition on the Estrous Cycle Deck (35):
What are the two nutritional states that can affect the estrous cycle?
What does short term severe under nutrition cause?
almost immediate decrease in GnRH and LH levels
(rapidly reversed when normal nutrition is restored)
What does long term malnourishment cause?
decrease in GnRH and LH levels
(starting them on normal ration will not always reverse)
Critical body fat hypothesis
a certain degree of fatness is necessary for normal reproduction
(12-14% for males, 22% for females)
Metabolic fuels hypothesis
acute changes in caloric availability can control GnRH secretion
What is leptin?
-peptide hormone secreted from white adipose tissue
-circulating levels are directly correlated with fat stores
How does leptin function as a permissive signal for pulsatiile secretory activity of GnRH neurons?
leptin inhibits NPY neurons that are in turn inhibitory on GnRH neurons
(by inhibiting the inhibitor, it allows GnRH secretion)
What happens when fat stores decline (in regards to leptin)?
circulating levels of leptin drop and the GnRH pulse generator is suppressed
What is ghrelin?
peptide hormone secreted by the stomach in an endocrine manner
(secretion increases with fasting, so it is a signal of energy insufficiency)
How does ghrelin function to suppress GnRH?
recent evidence suggests it suppresses the kisspeptin system and thus suppresses GnRH
What is insulin-like growth factor 1 (IGF-1)?
produced by the liver in response to growth hormone stimulation
How does IGF-1 function to increase GnRH?
can directly enhance secretion in GnRH neurons and can act indirectly by increasing kisspeptin secretion from KND neurons
What are the 2 parts of the metabolic fuels hypothesis
1. the fuel has to be present in the body in sufficient quantitiy
2. the fuel has to be available for oxidation in tissues
What is the most important fuel that the body is detecting?
What site detects the information about metabolic fuel oxidation?
area postrema (AP) located in the hindbrain
How does information from the hindbrain influence GnRH neurons?
-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
What do insulin and IGFs together promote?
granulosa cell proliferation and steroidogenesis
Falling IGF-1 during under nutrition results in what?
it has a potentially direct ovarian role in reducing cyclicity
What does an increase in nutrition results in?
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
Name and describe the 3 nutritional effects
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
What happens when glucose and insulin are increased?
-increased glucose uptake into follicles
-suppresses estradiol secretion from follicles
What happens when leptin is increased?
suppresses estradiol secretion from follicles
What happens when intrafollicular IGFBP is increased?
suppresses estradiol secretion from follicles
Suppression of estradiol secretion from follicles results in what?
less feedback inhibition of FSH secretion so more follicles are supported through the selection process
What is flushing?
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)
What are sodium ionophores and why would you use them?
alters rumen microflora to have propionate as the product of fermentation, which increases insulin and increases pituitary sensitivity to GnRH
(improved reproductive performance)
Why would you increase dietary fat?
results in increased propionate production and therefore improved reproductive performance
Why would you increase n-3 unsaturated fats?
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)
Low protein diets cause what?
cessation of estrous cycles in monogastrics
High protein diets cause what?
decrease oocyte quality with reductions in fertilization rates and blastocyst formation
Stress effects on breeding
-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
Stress effects on gestation
-crowing causes social stress which leads to immunocompromised animals
What are the effects of stress on tonic GnRH secretion?
-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
What are the effects of stress on generation of the LH surge?
-acute stress reduces GnRH secretion from the hypothalamus and no GnRH means no LH secretion