The effect of ractopamine on beta-adrenoceptor density and affinity in porcine adipose and skeletal muscle tissue. 1994

M E Spurlock, and J C Cusumano, and S Q Ji, and D B Anderson, and C K Smith, and D L Hancock, and S E Mills
Department of Animal Sciences, Purdue University, West Lafayette, IN 47907.

We have evaluated the effect of feeding ractopamine (Rac), a phenethanolamine lean enhancer being developed for commercial use in finishing pigs, on beta-adrenoceptor (beta-AR) number and ligand-receptor binding affinity in adipose and muscle tissues. Pigs weighing 78 +/- 1 kg were fed Rac (20 mg/kg of diet) for 0 (control), 1, 8, or 24 d before being killed at 105 +/- 1 kg BW. beta-adrenoceptor density (per milligram of protein) was decreased by Rac up to approximately 50% in both the middle and the outer layers of subcutaneous (SQ) adipose tissue. Orthogonal contrasts indicated significant (P < or = .05) linear effects of Rac in middle and outer SQ adipose tissue, and also a significant (P < or = .05) quadratic effect of Rac in the middle layer. Ractopamine did not affect the maximal binding (Bmax) of longissimus muscle. The relative affinity with which the beta-AR population of the tissues examined bound the radioligand ([3H]dihydroalprenolol) was not influenced by Rac. Likewise, feeding Rac had no effect on the affinity of the beta-AR for Rac. The data indicate that a Rac-induced reduction in the Bmax of adipose tissue may account for the diminished in vitro lipolytic potency of exogenous Rac after prolonged periods of Rac feeding, and that Rac-induced desensitization differs between adipose and skeletal muscle tissues.

UI MeSH Term Description Entries
D008024 Ligands A molecule that binds to another molecule, used especially to refer to a small molecule that binds specifically to a larger molecule, e.g., an antigen binding to an antibody, a hormone or neurotransmitter binding to a receptor, or a substrate or allosteric effector binding to an enzyme. Ligands are also molecules that donate or accept a pair of electrons to form a coordinate covalent bond with the central metal atom of a coordination complex. (From Dorland, 27th ed) Ligand
D008297 Male Males
D009132 Muscles Contractile tissue that produces movement in animals. Muscle Tissue,Muscle,Muscle Tissues,Tissue, Muscle,Tissues, Muscle
D010627 Phenethylamines A group of compounds that are derivatives of beta- aminoethylbenzene which is structurally and pharmacologically related to amphetamine. (From Merck Index, 11th ed) Phenylethylamines
D011869 Radioligand Assay Quantitative determination of receptor (binding) proteins in body fluids or tissue using radioactively labeled binding reagents (e.g., antibodies, intracellular receptors, plasma binders). Protein-Binding Radioassay,Radioreceptor Assay,Assay, Radioligand,Assay, Radioreceptor,Assays, Radioligand,Assays, Radioreceptor,Protein Binding Radioassay,Protein-Binding Radioassays,Radioassay, Protein-Binding,Radioassays, Protein-Binding,Radioligand Assays,Radioreceptor Assays
D011897 Random Allocation A process involving chance used in therapeutic trials or other research endeavor for allocating experimental subjects, human or animal, between treatment and control groups, or among treatment groups. It may also apply to experiments on inanimate objects. Randomization,Allocation, Random
D011941 Receptors, Adrenergic Cell-surface proteins that bind epinephrine and/or norepinephrine with high affinity and trigger intracellular changes. The two major classes of adrenergic receptors, alpha and beta, were originally discriminated based on their cellular actions but now are distinguished by their relative affinity for characteristic synthetic ligands. Adrenergic receptors may also be classified according to the subtypes of G-proteins with which they bind; this scheme does not respect the alpha-beta distinction. Adrenergic Receptors,Adrenoceptor,Adrenoceptors,Norepinephrine Receptor,Receptors, Epinephrine,Receptors, Norepinephrine,Adrenergic Receptor,Epinephrine Receptors,Norepinephrine Receptors,Receptor, Adrenergic,Receptor, Norepinephrine
D006133 Growth Substances Signal molecules that are involved in the control of cell growth and differentiation. Mitogens, Endogenous,Endogenous Mitogens
D000273 Adipose Tissue Specialized connective tissue composed of fat cells (ADIPOCYTES). It is the site of stored FATS, usually in the form of TRIGLYCERIDES. In mammals, there are two types of adipose tissue, the WHITE FAT and the BROWN FAT. Their relative distributions vary in different species with most adipose tissue being white. Fatty Tissue,Body Fat,Fat Pad,Fat Pads,Pad, Fat,Pads, Fat,Tissue, Adipose,Tissue, Fatty
D000318 Adrenergic beta-Agonists Drugs that selectively bind to and activate beta-adrenergic receptors. Adrenergic beta-Receptor Agonists,beta-Adrenergic Agonists,beta-Adrenergic Receptor Agonists,Adrenergic beta-Agonist,Adrenergic beta-Receptor Agonist,Betamimetics,Receptor Agonists, beta-Adrenergic,Receptors Agonists, Adrenergic beta,beta-Adrenergic Agonist,beta-Adrenergic Receptor Agonist,Adrenergic beta Agonist,Adrenergic beta Agonists,Adrenergic beta Receptor Agonist,Adrenergic beta Receptor Agonists,Agonist, Adrenergic beta-Receptor,Agonist, beta-Adrenergic,Agonist, beta-Adrenergic Receptor,Agonists, Adrenergic beta-Receptor,Agonists, beta-Adrenergic,Agonists, beta-Adrenergic Receptor,Receptor Agonist, beta-Adrenergic,Receptor Agonists, beta Adrenergic,beta Adrenergic Agonist,beta Adrenergic Agonists,beta Adrenergic Receptor Agonist,beta Adrenergic Receptor Agonists,beta-Agonist, Adrenergic,beta-Agonists, Adrenergic,beta-Receptor Agonist, Adrenergic,beta-Receptor Agonists, Adrenergic

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