Blood Metabolic Hormones and Leptin in Growing Lambs

Metabolic hormones such as insulin and thyroid hormones play an important role in animal metabolism. Insulin is a 5.8-kDa protein synthesized in the pancreatic β-cells and secreted in response to evaluation of plasma glucose level (Magistrelli et al., 2008). Insulin has an important role in glucose transport and modulates peripheral satiety signals and directly targets the central nervous system to inhibit food intake (Gale et al., 2004). Also, insulin has an important role in lipid metabolism, stimulating lipogenesis and inhibiting lipolysis (BanTokuda et al., 2008). The thyroid hormones maintain the homeostasis of energy and protein metabolism, thermoregulation, growth and productivity parameters (Huszenicza et al., 2002). Changes of blood thyroid hormone concentrations are an indirect measure changes in thyroid gland activity and circulating thyroid hormones. They can be considered as indicators of the metabolic and nutritional status of the animals (Todini et. al, 2007). Thyroxin (T4) and triiodothyronin (T3) are also factors that regulate leptin expression or its plasma concentration to some extent (Chilliard et al., 2005). Leptin is an “adipokine” peptide hormone produced by fat cells, particularly in white adipose tissue (Erhardt et al., 2003). There are many roles of leptin in the animal organism. Production of leptin is modulated by insulin, glucocorticoids and sexual steroids and affects on the central nervous system inhibiting hypothalamic neuropeptide production, mainly neuropeptide Y, which stimulate appetite (Stephens et al., 1995). The nutritional state is closely ISSN 1330-7142 UDK = 636.37.1:577.1