Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/2/2006
Publication Date: 6/1/2007
Citation: Ramsay, T.G., Richards, M.P. 2007. Beta-adrenergic regulation of uncoupling protein expression in swine. Comparative Physiology and Biochemistry A. 147(2):395-403. Interpretive Summary: The uncoupling proteins are thought to be involved in waste heat production, reducing the energy efficiency of growth in animals. Previous studies have detected their presence in swine and their regulation by the endocrine system. This study attempted to determine whether the sympathetic nervous system contributes to the regulation of the uncoupling proteins. A synthetic beta-adrenergic agonist, ractopamine, is commercially available and fed to swine to promote lean growth. The present study used ractopamine to determine if the sympathetic nervous system contributes to the regulation of uncoupling proteins 2 and 3. The data demonstrate that the uncoupling proteins are responsive to ractopamine treatment in finishing swine. Secondly, uncoupling protein response is specific to selected skeletal muscles. These results suggest the sympathetic nervous system may have a role, although limited, in the regulation of uncoupling proteins.
Technical Abstract: The present study was performed to examine the response of uncoupling protein (UCP) 2 and UCP3 genes to ractopamine treatment in finishing pigs. Seventeen crossbred barrows (Yorkshire x Landrace) were used in this study. Animals were individually fed a basal diet containing 18% CP, 1.2% lysine, and 3.5 Mcal of DE/kg ad libitum. At 80 kg, nine randomly selected pigs were presented with a diet supplemented with 10.0 ppm ractopamine. The other eight pigs were maintained on the standard diet (controls). Animals were fed ad libitum. Animals were maintained on treatment for 2 wk. A blood sample was obtained from each pig on d14 of treatment 6 h after feed presentation. Tissue samples were collected on d15, frozen in liquid nitrogen and stored at -80ºC prior to analysis for mRNA abundance. Total RNA was amplified by reverse transcription - PCR with subsequent quantification of transcripts by capillary electrophoresis with laser-induced fluorescence detection. Samples included outer subcutaneous adipose tissue, middle subcutaneous adipose tissue, leaf fat, liver, longissimus, semitendinosus red portion (STR) and semitendinosus white portion (STW). Dietary ractopamine had no effect on serum triglycerides (p = 0.793), non-esterified fatty acid (P = 0.174) or glucose (P = 0.414) concentrations relative to control pigs. Serum IGF-I (P = 0.908), insulin (P = 0.564), thyroxine (P = 0.248) and triiodothyronine (P = 0.923) concentrations were not affected by ractopamine treatment. Serum cortisol concentration was increased by 53% with ractopamine treatment but was not detectably different from controls (P = 0.063). UCP2 mRNA abundance was depressed in STW (P = 0.022) and STR (P < 0.001) by ractopamine feeding. Dietary ractopamine decreased UCP3 mRNA abundance by 28% in STW (P = 0.023) relative to feeding the control diet. The present data suggest that ractopamine or the metabolic adaptations to ractopamine have a role in regulating UCP2 and UCP3 expression in only selected muscles, with no apparent effect on adipose tissue.