Nutrition/stress on estrous/repro

Question 1

what does under-nutrition affect

Answer 1

• affects hypothalamus

- reduces GnRH secretion, which is reflected in pituitary/ovarian function

Question 2

what does increased nutrition do

Answer 2

• ovary is primary target

- H-P axis is secondarily affected by altered feedback

Question 3

short term energy restriction

Answer 3

• monogastrics: almost immediate decrease in GnRH and LH levels
• ruminants: same effect but takes several days
• effects are reversed when normal nutrition restored

Question 4

long term malnourishment

Answer 4

• starting on normal ration will not always quickly restore circulating gonadotropin levels or reproductive activity
• “critical body fat hypothesis” –> need some fat for reproduction (males 12-14%, females 22%)
• degree of adaptation available if kept at low body fat for a while

Question 5

what is leptin

Answer 5

• peptide hormone secreted from white adipose tissue
• circulating levels correlated with fat stores (more fat = more leptin)
• functions as a marker of long-term nutrition and relatively short-term metabolic changes

Question 6

leptin and reproductive system in good conditions

Answer 6

• leptin inhibits NPY neurons –> inhibitory directly and indirectly on GnRH
• leptin stimulates KNDy kisspeptin system –> stimulates GnRH pulses (low leptin decreases KNDy, kisspeptin, and therefore GnRH)

Question 7

what happens to leptin and GnRH when fat stores decline

Answer 7

circulating leptin levels drop and GnRH pulse generator is suppressed

Question 8

what is ghrelin

Answer 8

• peptide hormone secreted by stomach in endocrine manner
• secretion increases with fasting
• transient surge in anticipation of food
• circulating levels are inversely related to body condition (opposite of leptin)
• suppresses kisspeptin and therefore GnTH

Question 9

insulin-like growth factor 1 (IGF-1)

Answer 9

• fluctuations due to circulating levels produced by the liver in response to growth hormone stimulation
• directly enhances secretion by GnRH neurons, increases kiss secretion rom KNDy neurons
• levels decrease with restricted feeding

Question 10

insulin

Answer 10

• fluctuates in response to glucose
• overall concentration is directly proportional to amount of adipose tissue in the body
• inhibits NPY neurons

Question 11

gut fill?

Answer 11

• neural sensory inputs from GI tract via vagus nerve provide info on gut fill to control food intake
• minor role in controlling GnRH pulse generator?

Question 12

metabolic fuel hypothesis

Answer 12

• hinges on the body’s ability to detect changes in metabolic fuels that are available for oxidation
• the fuel (calories) has to be present in the body in sufficient quantity
• it has to be available for oxidation in tissues

Question 13

what are the fuels being detected in metabolic fuel hypothesis

Answer 13

• glucose (circulating and able to get into tissues)

- fatty acids

Question 14

what site(s) detect the information about metabolic fuel oxidation

Answer 14

area postrema (AP) located in the hindbrain –> inhibiting glucose oxidation here inhibits reproductive axis

Question 15

signaling the hypothalamo-pituitary axis

Answer 15

• GnRH neurons inhibited by neuronal transmission from hindbrain in at least 2 ways
  1) neuronal projections form hindbrain inhibit GnRH neurons directly using neuropeptide Y and catecholamines
  2) NPY and CA neurons activate CRH neurons –> inhibit GnRH neurons
  3) NPY suppresses KNDy neurons

Question 16

direct effects of energy deprivation on ovary (list)

Answer 16

• follicle growth
• oocyte viability
• CL function

Question 17

follicle growth during energy deprivation

Answer 17

• insulin and IGF-1 have synergistic action with gonadotropins
• GH increases, IGF-1 decreases –> reduces cyclicity

Question 18

oocyte viability during energy deprivation

Answer 18

-decreased fertilization rates and lower developmental competence

Question 19

CL function during energy deprivation

Answer 19

• small preovulatory follicles with poor steroidogenic capacity –> small, poorly steroidogenic CL
• exacerbated by low LH levels

Question 20

increasing energy to increase reproduction

Answer 20

• improving beyond normal does not stimulate H-P axis to further increase GnRH secretion
• positive influence is mediated at the ovarian/follicle level with some secondary input from the H-P axis
• 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 21

3 divisions of nutritional effects

Answer 21

• acute effect: seen before body weight change is detectable
• dynamic effect: seen while body weight is increasing
• static effect: seen when body weight is maintained at a high level

Question 22

what happens to hormones during conditions of acutely increased nutrition

Answer 22

• glucose/insulin increased –> increased glucose uptake into follicles –> suppresses estradiol secretion from follicles
• leptin increased –> suppresses estradiol secretion from follicles
• IGFBP increased –> less free IGF –> suppresses estradiol secretion from follicles

Question 23

result of decreased estradiol production from follicles during increased nutrition

Answer 23

less feedback inhibition of FSH –> FSH levels higher –> more follicles supported

Question 24

flushing

Answer 24

• increases ovulation rate in sheep
• slightly undernourished ewes put on a high plane of nutrition 2-3wks prior to breeding
• allows them to achieve but not exceed their genetic potential

Question 25

sodium ionophores (monensin)

Answer 25

- alters rumen microflora and shifts away from acetate/butyrate towards propionate - propionate is gluconeogenic --> increases insulin - increases pituitary sensitivity to GnRH and improve reproductive performance

Question 26

dietary fat

Answer 26

- feeding some fat to ruminants increases propionate production (gluconeogenic) - increases medium sized follicle population, improves breeding performance - ratio of n6:n3 unsaturated fats are important - high n-3 can reduce prostaglandin/sensitivity to it --> longer estrous cycle, increased embryo survival

Question 27

protein

Answer 27

- low protein diets cause cessation of estrous cycles in monogastrics - specific amino acid deficiencies are important in monogastrics - ruminants: excess protein and NPN result in increased urea and ammonia levels --> no effect on cyclicity

Question 28

other nutritional influences

Answer 28

- vitamin/mineral deficiencies cause embryonic and neonatal losses - Cu, I deficiencies cause irregular/suppressed estrous cyclicity

Question 29

examples of stress effects on reproduction

Answer 29

- cows/ewes: reduced GnRH, LH after shipping - captive wild animals: high cortisol, low sex steroids - change in social status - IVF patients

Question 30

stress and gestation

Answer 30

pregnant women stressed at 28-30wks shortens pregnancy and lowers birth weight

Question 31

hypothalamic effects of stress

Answer 31

- release of CRH and vasopressin - CRH predominates in response to weak stress - vasopressin secreted with CRH with more intense stress - most of inhibitory effects mediated by activation of inhibitory interneurons --> use opioids and GABA to affect activation of GnRH neurons

Question 32

effects of stress on generation of LH surge

Answer 32

- acute stress can prevent occurrence of pre-ovulatory LH surge - less severe stressors can delay its occurrence and decrease its amplitude - effects represent a combination of reduced GnRH secretion from hypothalamus and reduced LH secretion in response to GnRH

Question 33

overriding inhibition of stress (when it's a good idea)

Answer 33

- old individuals - seasonal breeders - both partners provide parental care - semelparous species (die after breeding) - dominant animals where only dominant animals breed and dominance is temporary