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Naves Aroeira C, Feddern V, Gressler V, Contreras-Castillo CJ, Hopkins DL. Growth Promoters in Cattle and Pigs: A Review of Legislation and Implications for Human Health. FOOD REVIEWS INTERNATIONAL 2021. [DOI: 10.1080/87559129.2021.1961268] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Carolina Naves Aroeira
- Departamento de Zootecnia, Universidade de São Paulo, Escola Superior de Agricultura “Luiz de Queiroz”, Piracicaba, Brazil
| | | | | | | | - David Laurence Hopkins
- NSW Department of Primary Industries, Centre for Red Meat and Sheep Development, Cowra, New South Wales, Australia
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Dilger AC, Johnson BJ, Brent P, Ellis RL. Comparison of beta-ligands used in cattle production: structures, safety, and biological effects. J Anim Sci 2021; 99:6333506. [PMID: 34337648 PMCID: PMC8326055 DOI: 10.1093/jas/skab094] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 03/22/2021] [Indexed: 11/14/2022] Open
Abstract
Technologies that increase the efficiency and sustainability of food animal production to provide meat for a growing population are necessary and must be used in a manner consistent with good veterinary practices, approved labeled use, and environmental stewardship. Compounds that bind to beta-adrenergic receptors (β-AR), termed beta-adrenergic receptor ligands (β-ligands), are one such technology and have been in use globally for many years. Though all β-ligands share some similarities in structure and function, the significance of their structural and pharmacological differences is sometimes overlooked. Structural variations in these molecules can affect absorption, distribution, metabolism, and excretion as well as cause substantial differences in biological and metabolic effects. Several β-ligands are available for use specifically in cattle production. Ractopamine and zilpaterol are beta-adrenergic agonists approved to increase weight gain, feed efficiency, and carcass leanness in cattle. They both bind to and activate β1- and β2-AR. Lubabegron is a newly developed selective beta-adrenergic modulator with unique structural and functional features. Lubabegron displays antagonistic behavior at the β1- and β2-AR but agonistic behavior at the β3-AR. Lubabegron is approved for use in cattle to reduce ammonia emissions per unit of live or carcass weight. Additionally, lubabegron can withstand prolonged use as the β3-AR lacks structural features needed for desensitization. Due to these unique features of lubabegron, this new β-ligand provides an additional option in cattle production. The individual properties of each β-ligand should be considered when making risk management decisions, as unique properties result in varying human food safety profiles that can determine appropriate safe β-ligand use.
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Affiliation(s)
- Anna C Dilger
- Department of Animal Sciences, University of Illinois, Urbana-Champaign, Urbana, IL, USA
- Corresponding author:
| | - Bradley J Johnson
- Department of Animal and Food Sciences, Texas Tech University, Lubbock, TX, USA
| | - Paul Brent
- University of Laval, Quebec, QC, Canada
- Global Risk Assessment and Risk Management Solutions, Queensland, Australia
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Justo M, Nascimento LA, Meneses Y, Trombeta T, Cohen S. Monogenoidea parasites of Oreochromis niloticus submitted to ractopamine supplemented diet from cultivated system. ARQ BRAS MED VET ZOO 2020. [DOI: 10.1590/1678-4162-11652] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
ABSTRACT Oreochromis niloticus (Linnaeus) (Perciformes: Cichlidae), commonly named “tilapia”, is the second most cultivated species in the world. Among the diseases that affect tilapia are parasitic diseases caused by parasites of the class Monogenoidea. The aim of the present study was to analyze parasitism rates among specimens of O. niloticus in farming systems, after dietary supplementation with ractopamine, a growth promoter that is used for fattening fish. The action of this substance on the quantitative parameters of infestation by Monogenoidea was evaluated. Samples of O. niloticus were obtained from a fish farm in Brasília, Federal District, Brazil. Their gills were removed and fixed. Four species of monogenoideans were collected: Cichlidogyrus halli, C. sclerosus, C. thurstonae and Scutogyrus longicornis. The results from this study indicate that the monogenoidean parasites of tilapias examined here presented different behaviors in relation to the ractopamine concentrations that were added to the food. The parasitological indexes did not present significant reductions through using ractopamine, thus leading to the conclusion that administration of ractopamine is not efficient as a method for controlling infestations of monogenoidean parasites.
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Affiliation(s)
| | | | | | - T. Trombeta
- Universidade Federal do Oeste do Pará, Brazil
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Aroeira CN, Feddern V, Gressler V, Molognoni L, Daguer H, Dalla Costa OA, de Lima GJ, Contreras-Castillo CJ. Determination of ractopamine residue in tissues and urine from pig fed meat and bone meal. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2019; 36:424-433. [DOI: 10.1080/19440049.2019.1567942] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Carolina N. Aroeira
- Departamento de Zootecnia, Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo, Piracicaba, Brazil
| | - Vivian Feddern
- Centro Nacional de Pesquisa em Suínos e Aves, Embrapa Suínos e Aves, Concórdia, Brazil
| | - Vanessa Gressler
- Centro Nacional de Pesquisa em Suínos e Aves, Embrapa Suínos e Aves, Concórdia, Brazil
| | - Luciano Molognoni
- Ministério da Agricultura, Pecuária e Abastecimento, Laboratório Nacional Agropecuário (Lanagro/RS), São José, Brazil
| | - Heitor Daguer
- Ministério da Agricultura, Pecuária e Abastecimento, Laboratório Nacional Agropecuário (Lanagro/RS), São José, Brazil
| | - Osmar A. Dalla Costa
- Centro Nacional de Pesquisa em Suínos e Aves, Embrapa Suínos e Aves, Concórdia, Brazil
| | | | - Carmen J. Contreras-Castillo
- Departamento de Zootecnia, Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo, Piracicaba, Brazil
- Departamento de Agroindústria, Alimentos e Nutrição, Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo, Piracicaba, Brazil
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So EC, Foo NP, Ko SY, Wu SN. Bisoprolol, Known to Be a Selective β₁-Receptor Antagonist, Differentially but Directly Suppresses I K(M) and I K(erg) in Pituitary Cells and Hippocampal Neurons. Int J Mol Sci 2019; 20:E657. [PMID: 30717422 PMCID: PMC6386942 DOI: 10.3390/ijms20030657] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Revised: 01/27/2019] [Accepted: 01/30/2019] [Indexed: 12/27/2022] Open
Abstract
Bisoprolol (BIS) is a selective antagonist of β₁ adrenergic receptors. We examined the effects of BIS on M-type K⁺ currents (IK(M)) or erg-mediated K⁺ currents (IK(erg)) in pituitary GH3, R1220 cells, and hippocampal mHippoE-14 cells. As GH₃ cells were exposed to BIS, amplitude of IK(M) was suppressed with an IC50 value of 1.21 μM. The BIS-induced suppression of IK(M) amplitude was not affected by addition of isoproterenol or ractopamine, but attenuated by flupirtine or ivabradine. In cell-attached current, BIS decreased the open probability of M-type K⁺ (KM) channels, along with decreased mean opening time of the channel. BIS decreased IK(erg) amplitude with an IC50 value of 6.42 μM. Further addition of PD-118057 attenuated BIS-mediated inhibition of IK(erg). Under current-clamp conditions, BIS depolarization increased the firing of spontaneous action potentials in GH₃ cells; addition of flupirtine, but not ractopamine, reversed BIS-induced firing rate. In R1220 cells, BIS suppressed IK(M); subsequent application of ML-213(Kv7.2 channel activator) reversed BIS-induced suppression of the current. In hippocampal mHippoE-14 neurons, BIS inhibited IK(M) to a greater extent compared to its depressant effect on IK(erg). This demonstrated that in pituitary cells and hippocampal neurons the presence of BIS is capable of directly and differentially suppressing IK(M) and IK(erg), despite its antagonism of β₁-adrenergic receptors.
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Affiliation(s)
- Edmund Cheung So
- Department of Anesthesia, An Nan Hospital, China Medical University, Tainan 70965, Taiwan.
- Department of Anesthesia, China Medical University, Taichung 40402, Taiwan.
- Graduate Institute of Medical Sciences, Chang Jung Christian University, Tainan 71101, Taiwan.
| | - Ning-Ping Foo
- Department of Anesthesia, An Nan Hospital, China Medical University, Tainan 70965, Taiwan.
- Graduate Institute of Medical Sciences, Chang Jung Christian University, Tainan 71101, Taiwan.
- Department of Emergency Medicine, An Nan Hospital, China Medical University, Tainan 70965, Taiwan.
| | - Shun Yao Ko
- Graduate Institute of Medical Sciences, Chang Jung Christian University, Tainan 71101, Taiwan.
| | - Sheng-Nan Wu
- Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan 70101, Taiwan.
- Department of Physiology, National Cheng Kung University Medical College, Tainan 70101, Taiwan.
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Feldpausch JA, Amachawadi RG, Tokach MD, Scott HM, Nagaraja TG, Dritz SS, Goodband RD, Woodworth JC, DeRouchey JM. Effects of dietary copper, zinc, and ractopamine hydrochloride on finishing pig growth performance, carcass characteristics, and antimicrobial susceptibility of enteric bacteria12. J Anim Sci 2016; 94:3278-3293. [DOI: 10.2527/jas.2016-0340] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Costa-Lima BR, Suman SP, Li S, Beach CM, Silva TJ, Silveira ET, Bohrer BM, Boler DD. Dietary ractopamine influences sarcoplasmic proteome profile of pork Longissimus thoracis. Meat Sci 2015; 103:7-12. [DOI: 10.1016/j.meatsci.2014.12.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 08/27/2014] [Accepted: 12/19/2014] [Indexed: 11/29/2022]
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8
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Almeida V, Nuñez A, Schinckel A, Ward M, Andrade C, Sbardella M, Berenchtein B, Coutinho L, Miyada V. Gene expression of beta-adrenergic receptors and myosin heavy chain isoforms induced by ractopamine feeding duration in pigs not carrying the ryanodine receptor mutation. Livest Sci 2015. [DOI: 10.1016/j.livsci.2014.12.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Liu X, Grandy DK, Janowsky A. Ractopamine, a livestock feed additive, is a full agonist at trace amine-associated receptor 1. J Pharmacol Exp Ther 2014; 350:124-9. [PMID: 24799633 DOI: 10.1124/jpet.114.213116] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Ractopamine (RAC) is fed to an estimated 80% of all beef, swine, and turkey raised in the United States. It promotes muscle mass development, limits fat deposition, and reduces feed consumption. However, it has several undesirable behavioral side effects in livestock, especially pigs, including restlessness, agitation, excessive oral-facial movements, and aggressive behavior. Numerous in vitro and in vivo studies suggest RAC's physiological actions begin with its stimulation of β1- and β2-adrenergic receptor-mediated signaling in skeletal muscle and adipose tissue; however, the molecular pharmacology of RAC's psychoactive effects is poorly understood. Using human cystic fibrosis transmembrane conductance regulator (hCFTR) chloride channels as a sensor for intracellular cAMP, we found that RAC and p-tyramine (TYR) produced concentration-dependent increases in chloride conductance in oocytes coexpressing hCFTR and mouse trace amine-associated receptor 1 (mTAAR1), which was completely reversed by the trace amine-associated receptor 1 (TAAR1)-selective antagonist EPPTB [N-(3-ethoxyphenyl)-4-pyrrolidin-1-yl-3-trifluoromethylbenzamide]. Oocytes coexpressing hCFTR and the human β2-adrenergic receptor showed no response to RAC or TYR. These studies demonstrate that, contrary to expectations, RAC is not an agonist of the human β2-adrenergic receptor but rather a full agonist for mTAAR1. Since TAAR1-mediated signaling can influence cardiovascular tone and behavior in several animal models, our finding that RAC is a full mTAAR1 agonist supports the idea that this novel mechanism of action influences the physiology and behavior of pigs and other species. These findings should stimulate future studies to characterize the pharmacological, physiological, and behavioral actions of RAC in humans and other species exposed to this drug.
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Affiliation(s)
- Xuehong Liu
- Department of Physiology and Pharmacology, School of Medicine (X.L., D.K.G.), Knight Cardiovascular Institute (D.K.G.), Research Service, Department of Veterans Affairs Medical Center, and Departments of Psychiatry and Behavioral Neuroscience (A.J.), and The Methamphetamine Abuse Research Center (D.K.G., A.J.), Oregon Health and Science University, Portland, Oregon
| | - David K Grandy
- Department of Physiology and Pharmacology, School of Medicine (X.L., D.K.G.), Knight Cardiovascular Institute (D.K.G.), Research Service, Department of Veterans Affairs Medical Center, and Departments of Psychiatry and Behavioral Neuroscience (A.J.), and The Methamphetamine Abuse Research Center (D.K.G., A.J.), Oregon Health and Science University, Portland, Oregon
| | - Aaron Janowsky
- Department of Physiology and Pharmacology, School of Medicine (X.L., D.K.G.), Knight Cardiovascular Institute (D.K.G.), Research Service, Department of Veterans Affairs Medical Center, and Departments of Psychiatry and Behavioral Neuroscience (A.J.), and The Methamphetamine Abuse Research Center (D.K.G., A.J.), Oregon Health and Science University, Portland, Oregon
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Almeida VV, Nuñez AJC, Schinckel AP, Andrade C, Balieiro JCC, Sbardella M, Miyada VS. Time-response relationship of ractopamine feeding on growth performance, plasma urea nitrogen concentration, and carcass traits of finishing pigs1. J Anim Sci 2013; 91:811-8. [DOI: 10.2527/jas.2012-5372] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- V. V. Almeida
- Department of Animal Science, University of São Paulo, Piracicaba, 13418-900, Brazil
| | - A. J. C. Nuñez
- Department of Animal Science, University of São Paulo, Pirassununga, 13635-900, Brazil
| | - A. P. Schinckel
- Department of Animal Sciences, Purdue University, West Lafayette, IN 47907
| | - C. Andrade
- Department of Animal Science, University of São Paulo, Piracicaba, 13418-900, Brazil
| | - J. C. C. Balieiro
- Department of Basic Science, University of São Paulo, Pirassununga, 13635-900, Brazil
| | - M. Sbardella
- Department of Animal Science, University of São Paulo, Piracicaba, 13418-900, Brazil
| | - V. S. Miyada
- Department of Animal Science, University of São Paulo, Piracicaba, 13418-900, Brazil
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11
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Key signalling factors and pathways in the molecular determination of skeletal muscle phenotype. Animal 2012; 1:681-98. [PMID: 22444469 DOI: 10.1017/s1751731107702070] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The molecular basis and control of the biochemical and biophysical properties of skeletal muscle, regarded as muscle phenotype, are examined in terms of fibre number, fibre size and fibre types. A host of external factors or stimuli, such as ligand binding and contractile activity, are transduced in muscle into signalling pathways that lead to protein modifications and changes in gene expression which ultimately result in the establishment of the specified phenotype. In skeletal muscle, the key signalling cascades include the Ras-extracellular signal regulated kinase-mitogen activated protein kinase (Erk-MAPK), the phosphatidylinositol 3'-kinase (PI3K)-Akt1, p38 MAPK, and calcineurin pathways. The molecular effects of external factors on these pathways revealed complex interactions and functional overlap. A major challenge in the manipulation of muscle of farm animals lies in the identification of regulatory and target genes that could effect defined and desirable changes in muscle quality and quantity. To this end, recent advances in functional genomics that involve the use of micro-array technology and proteomics are increasingly breaking new ground in furthering our understanding of the molecular determinants of muscle phenotype.
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12
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Physiopathological changes related to the use of ractopamine in swine: Clinical and pathological investigations. Livest Sci 2012. [DOI: 10.1016/j.livsci.2011.10.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Poletto R, Cheng HW, Meisel RL, Garner JP, Richert BT, Marchant-Forde JN. Aggressiveness and brain amine concentration in dominant and subordinate finishing pigs fed the β-adrenoreceptor agonist ractopamine12. J Anim Sci 2010; 88:3107-20. [DOI: 10.2527/jas.2009-1876] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Kim HK, Della-Fera MA, Hausman DB, Baile CA. Effect of clenbuterol on apoptosis, adipogenesis, and lipolysis in adipocytes. J Physiol Biochem 2010; 66:197-203. [DOI: 10.1007/s13105-010-0024-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2010] [Accepted: 05/13/2010] [Indexed: 11/28/2022]
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Poletto R, Meisel RL, Richert BT, Cheng HW, Marchant-Forde JN. Behavior and peripheral amine concentrations in relation to ractopamine feeding, sex, and social rank of finishing pigs1. J Anim Sci 2010; 88:1184-94. [DOI: 10.2527/jas.2008-1576] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Poletto R, Rostagno MH, Richert BT, Marchant-Forde JN. Effects of a “step-up” ractopamine feeding program, sex, and social rank on growth performance, hoof lesions, and Enterobacteriaceae shedding in finishing pigs1. J Anim Sci 2009; 87:304-13. [DOI: 10.2527/jas.2008-1188] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Effect or ractopamine on growth and body composition of pigs during compensatory growth. Animal 2009; 3:173-80. [DOI: 10.1017/s1751731108003285] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Gonzalez JM, Dijkhuis RD, Johnson DD, Carter JN, Johnson SE. Differential response of cull cow muscles to the hypertrophic actions of ractopamine-hydrogen chloride1. J Anim Sci 2008; 86:3568-74. [DOI: 10.2527/jas.2008-1049] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Ramsay TG, Richards MP. Beta-adrenergic regulation of uncoupling protein expression in swine. Comp Biochem Physiol A Mol Integr Physiol 2007; 147:395-403. [PMID: 17383207 DOI: 10.1016/j.cbpa.2007.01.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2006] [Revised: 01/11/2007] [Accepted: 01/11/2007] [Indexed: 11/28/2022]
Abstract
This study examined the beta-adrenergic regulation of uncoupling protein (UCP) 2 and UCP3 gene expression in porcine tissues. In vitro experiments examined changes in UCP2 and UCP3 gene expression in middle (MSQ) and outer (OSQ) subcutaneous adipose tissues from crossbred neutered male pigs. Incubation of tissue slices (24 h) with 0 to 1000 nM isoproterenol increased UCP2 and UCP3 mRNA abundance in MSQ and OSQ, relative to 18S rRNA (P<0.05). For the in vivo experiment, nine randomly selected pigs (80 kg) were presented with a diet supplemented with 10.0 ppm ractopamine for 2 weeks. Another eight pigs were maintained on a control diet. Dietary ractopamine did not affect adipose UCP2 or UCP3 gene expression (P>0.05). However, UCP2 mRNA abundance was depressed in semitendinosus white (STW, P<0.05) and semitendinosus red (STR, P<0.001) by ractopamine feeding. Also, ractopamine decreased UCP3 mRNA abundance by 28% in STW (P<0.05). The in vitro data suggest that beta-adrenergic agonists directly affect adipose tissue UCP expression, although these adipose effects can be masked by the in vivo physiology. The in vivo data indicate that beta-adrenergic agonists may function in regulating UCP2 and UCP3 expression in selected muscles.
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Affiliation(s)
- T G Ramsay
- Growth Biology Laboratory, USDA-ARS, Beltsville, MD 20705, USA.
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Dugan SG, Lortie MB, Nickerson JG, Moon TW. Regulation of the rainbow trout (Oncorhynchus mykiss) hepatic beta2-adrenoceptor by adrenergic agonists. Comp Biochem Physiol B Biochem Mol Biol 2004; 136:331-42. [PMID: 14529759 DOI: 10.1016/s1096-4959(03)00217-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The characteristics of hepatic beta(2)-adrenoceptors (AR) were examined in rainbow trout (Oncorhynchus mykiss) chased once per day to exhaustion for up to 7 days or fed the repartitioning agents clenbuterol (CLEN) or ractopamine (RACT) that function in mammals as beta-agonists. A one-day chase and feeding the CLEN for 37 days resulted in a significant 27% and 33% decrease, respectively, in the number of CGP-binding sites (B(max)) with no significant change in affinity (Kd) of hepatic beta(2)-ARs. Despite the significant decrease in beta(2)-AR numbers with CLEN feeding, no significant differences were found for either beta(2)-AR mRNA levels or adenylyl cyclase (ACase) activities. In addition, CLEN displayed only partial agonist activities as it was found to be more effective at blocking isoproterenol-stimulated cAMP production in isolated hepatocytes than stimulating cAMP production. The small affects of RACT may be related to its low active stereoisomer content and low affinity for the trout beta(2)-AR. Agonist regulation of the trout hepatic beta(2)-ARs may involve down-regulation of the receptors without affecting responsiveness.
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Affiliation(s)
- Stephen G Dugan
- Department of Biology, University of Ottawa, 150 Louis Pasteur, Ottawa, ON, Canada K1N 6N5
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