ENDOCRINE REGULATION OF GROWTH AND METABOLISM IN THE PIG - A REVIEW

The endocrine system has to balance the counteracting processes of protein synthesis and degradation. Moreover, it has to ensure that the increase in muscle mass is also balanced with other physiological requirements. Growth hormone (GH) stimulates protein synthesis indirectly by favouring IGF-I release by the liver and influences energy distribution according to food intake by either inhibiting lipogenesis or stimulating Lipolysis. Glucose modifies the system by influencing GH release from the pituitary and by its role for IGF-I release from the liver. Gonadal steroids participate in the regulation of metabolism. Androgens protect the muscles against excessive degradation (anticatabolic function). Oestrogens, both from the ovary and the testes, stimulate GH and IGF-I release. Oestrogens and androgens additionally decrease food intake dose dependently. These regulatory principles are important for the survival strategy of wild boars. Decreasing photoperiod optimizes reproductive functions in autumn/winter. During that time food intake is minimal and uncouples IGF-I from GH. The lipolytic function of GH provides energy for maintenance and the anticatabolic action of androgens protects muscles against excessive protein degradation. During summer, GH and IGF-I are increased by the photoperiod and high food intake permits an improved anabolic situation.