A novel function of lamb and pork: Different effects of lamb and pork consumption on thyroid hormone levels and energy metabolism of Sprague-Dawley rats

Different effects of lamb and pork consumption on thyroid hormone levels and energy metabolism of rats were investigated. Three diets, a lamb meat diet (LD), a pork meat diet (PD) and control casein diet (CD) were isocaloric (15.5 kJ/g dry matters). Rats in the PD group had higher serum selenium concentrations (P < 0.05) and liver 5′-deiodinase activities (P < 0.05), caused by higher selenium contents in pork meat (PM). As a result, PM consumption increased serum tri-iodothryonine (T3) concentrations (P < 0.05) and decreased serum thyroxine (T4) concentrations compared to casein and lamb meat (LM). Compared to casein and LM powder, PM powder had higher total content of glutamic acid, leucine, aspartic acid, serine, and alanine (48.94 vs 44.24 vs 44.78), which led to higher serum TBG concentrations (P < 0.05) in the PD group. Compared to casein, PM powder had higher total content of leucine and isoleucine (9.87 vs 9.21; 5.12 vs 4.74), LM powder had lower content of leucine (8.14 vs 9.21) leading to higher serum albumin concentrations in the PD group (P < 0.05) and lower ones in the LD group (P < 0.05). Consequently, the PD group had lower serum concentrations of free T4 (FT4) and free T3 (FT3) (P < 0.05), thus significantly decreasing the energy expenditure of rats, while the LD group had higher serum FT3 concentrations (P < 0.05), thus significantly increasing the energy expenditure. These were deduced from the different changes of Na,K-ATPase activities of liver and skeletal muscle (P < 0.05), oxygen consumption rates (OCRs) (P < 0.05) and rectal temperature, especially on day 13 (P < 0.05) and the body weights (P < 0.05) in the PD or LD group. We concluded that PM or LM consumption, with different amino acids composition, had different effects on the energy metabolism of rats by multiple-step regulation of THs.