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

E-ISSN： 1475-2662|68|3|667-676

ISSN： 0007-1145

Source： British Journal of Nutrition, Vol.68, Iss.3, 1992-11, pp. : 667-676

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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 (T₃)/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 T₃ 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, T₃ 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 T₃ and in vitro ouabain decrease lipogenesis, but, when combined, the effects are not cumulative