In vitro lipid metabolism, growth and metabolic hormone concentrations in hyperthyroid chickens

Abstract

Indian River male broiler chickens growing from 7 to 28 d of age were fed on diets containing energy: protein values varying from 43 to 106 MJ/kg protein and containing 0 or 1 mg triiodothyronine (T 3 )/kg diet to study effects on growth, metabolic hormone concentrations and in vitro lipogenesis. In vitro lipid synthesis was determined in liver explants in the presence and absence of ouabain (Na + , K + -transporting ATPase ( EC 3.6.1.37) inhibitor) to estimate the role of enzyme activity in explants synthesizing lipid. Growth and feed consumption increased ( P < 0.01) when the energy: protein value decreased from 106 to 71 MJ/kg protein; however, both variables decreased as the value was further decreased from 53 to 43 MJ/kg protein. Triiodothyronine depressed ( P < 0.01) growth, but not food intake. Large energy:protein diets (> 53 MJ/kg protein) and dietary T 3 lowered ( P < 0.01) plasma growth hormone. Large energy:protein diets (> 53 MJ/kg protein) increased ( P < 0.01) lipogenesis, plasma growth hormone (GH) and decreased plasma insulin-like growth factor 1 (IGF-1). Also, T 3 decreased plasma GH, IGF-1 in vitro lipogenesis. Ouabain inhibited a greater proportion of in vitro lipogenesis in those explants synthesizing fat at a high rate. Both dietary T 3 and in vitro ouabain decrease lipogenesis, but, when combined, the effects are not cumulative