1. Suporn Katawatin Khon Kaen University
Lactotrophic axis
Suporn Katawatin
Khon Kaen University

2. Mammary gland, mammary development, milk production
TRH
Dopamine
Hypothalamus _ +
Prolactin
Pituitary
Mammary gland, mammary development, milk production
Target tissue/effects
Lactation
Biological function

3. Prolactin Suppress by hypothalamic dopamine
Stimulate by TRH, neurophysin, substance P
Primary function: stimulate milk synthesis and secretion
Other functions: effect on CL, salt-water balance, immunity, growth, development and metabolism (Bazer, 1991; Weigent, 1996)

4. Stress- induced PRL Stress lead to hyperprolactinemia
Acute psychological stress increase PRL (Matthews & Parrott, 1994)
Aggressive, fighting, oppositive behaviour increase PRL (Matthews & Parrott, 1994)

5. Adaptive purpose to stress-induced PRL
PRL may enhance active avoidance behavior, induce analgesia and offer protection against chronic stress effects (Drago et al., 1989)

6. Thermal stress
PRL positive related to ambient temperature (Wettemann & Tucker, 1974)
PRL reduces in cold exposure
Stimulatory dopamine signaling within the ventromedial hypothalamus is involved with elevated PRL release due to heat exposure

7. Reduce PRL secretion PRL responses to stress are mostly increase
Reduced PRL occur in prolonged illness, this may be caused by the disease or decrease in food intake
Fasting reduces PRL in pigs, rats and humans (Rojkittikhun et al., 1993)

8. Gonadotrophic Axis

9. Gonads, sperm & egg, sex steroid secretion
GnRH
Hypothalamus
Gonadotrophin LH/FSH
Pituitary
Gonads, sperm & egg, sex steroid secretion
Target tissue, effects
Biological function
Reproduction

10. Selye (1939) : in cases of emergency, pituitary tends to produce more ACTH and less gonadotropin
Life maintaining principle of adrenal cortex is more necessary than preservation of normal sex function
Chronic stress decrease LH, FSH and reproductive failure (Moberg, 1991)
Glucocorticoids, vasopressin, ACTH, opioids, CRH suppressed gonadotropin secretion (Dobson and Smith, 1995)
Glucocorticoids inhibit gonadal steroids and responsiveness to sex steroids (Magiakou et al., 1997)

11. Nutritional stress Undernutrition … Delay or prevent onset of puberty
interfere normal cyclicity in female and cause infertility in males
decreased gonadotropin secretion by reduced GnRH

12. Leptin : hormone produced in fat tissue
Required for reproduction (Houseknecht et al., 1998)
Reduced leptin due to undernutrition may play important role in disruption of reproductive neuroendocrine function (Nagatani et al., 1998)

13. Thermal stress Heat stress inhibit gonadotropin secretion
Heat exposure reduce GnRH release and responsiveness of pituitary gland to GnRH (Gilad et al., 1993)

14. Cold stress Long-term below TNZ reduces LH, FSH
may reflect inadequate nutrition relative to increased metabolic demand at colder temperatures
Reduction in leptin (low appetite) during cold stress would be expected to suppress reproductive neuroendocrine axis

15. Thyrotrophic Axis

16. Metabolic rate, thermogenesis
TRH
Somatostatin
Hypothalamus _ +
TSH
Pituitary
Thyroid, T3, T4 secretion
Target tissue, effects
Metabolic rate, thermogenesis
Biological function

17. Thyroid hormones & Thermal stress
Potent metabolic regulators
Control body temp. and metabolism
responds to changes in thermogenic demand
cool temp. increase activity of thyroid axis (Arancibia et al., 1996)
Exposure to cold increase TRH gene expression and secretion (Joseph-Bravo et al., 1998)

18. Nutritional stress Decreases overall activity of thyroid axis
reflects an important adaptive response to undernutrition
Chronic undernutrition elevate HPA activity
may due to suppressed activity of thyroid axis; on TSH secretion, thyrotroph function, TRH release, thyroid hormone production and its receptors
Reduction in metabolic rate and associated energy use has a positive survival value at times when food supply is limited (Chillard et al., 1998)