Suporn Katawatin Khon Kaen University Lactotrophic axis Suporn Katawatin Khon Kaen University

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

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)

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

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)

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

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)

Gonadotrophic Axis

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

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)

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

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)

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

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

Thyrotrophic Axis

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

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)

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)