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Reis-Costa A, Belew GD, Viegas I, Tavares LC, Meneses MJ, Patrício B, Gastaldelli A, Macedo MP, Jones JG. The Effects of Long-Term High Fat and/or High Sugar Feeding on Sources of Postprandial Hepatic Glycogen and Triglyceride Synthesis in Mice. Nutrients 2024; 16:2186. [PMID: 39064628 PMCID: PMC11279633 DOI: 10.3390/nu16142186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2024] [Revised: 07/03/2024] [Accepted: 07/06/2024] [Indexed: 07/28/2024] Open
Abstract
BACKGROUND In MASLD (formerly called NAFLD) mouse models, oversupply of dietary fat and sugar is more lipogenic than either nutrient alone. Fatty acids suppress de novo lipogenesis (DNL) from sugars, while DNL inhibits fatty acid oxidation. How such factors interact to impact hepatic triglyceride levels are incompletely understood. METHODS Using deuterated water, we measured DNL in mice fed 18-weeks with standard chow (SC), SC supplemented with 55/45-fructose/glucose in the drinking water at 30% (w/v) (HS), high-fat chow (HF), and HF with HS supplementation (HFHS). Liver glycogen levels and its sources were also measured. For HS and HFHS mice, pentose phosphate (PP) fluxes and fructose contributions to DNL and glycogen were measured using [U-13C]fructose. RESULTS The lipogenic diets caused significantly higher liver triglyceride levels compared to SC. DNL rates were suppressed in HF compared to SC and were partially restored in HFHS but supplied a minority of the additional triglyceride in HFHS compared to HF. Fructose contributed a significantly greater fraction of newly synthesized saturated fatty acids compared to oleic acid in both HS and HFHS. Glycogen levels were not different between diets, but significant differences in Direct and Indirect pathway contributions to glycogen synthesis were found. PP fluxes were similar in HS and HFHS mice and were insufficient to account for DNL reducing equivalents. CONCLUSIONS Despite amplifying the lipogenic effects of fat, the fact that sugar-activated DNL per se barely contributes suggests that its role is likely more relevant in the inhibition of fatty acid oxidation. Fructose promotes lipogenesis of saturated over unsaturated fatty acids and contributes to maintenance of glycogen levels. PP fluxes associated with sugar conversion to fat account for a minor fraction of DNL reducing equivalents.
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Affiliation(s)
- Ana Reis-Costa
- PhD Programme in Experimental Biology and Biomedicine, Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal; (A.R.-C.); (G.D.B.)
- Center for Neuroscience and Cell Biology (CNC-UC), Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal
- Grupo de Estudos de Investigação Fundamental e Translacional (GIFT) da Sociedade Portuguesa de Diabetologia, 1250-198 Lisboa, Portugal
| | - Getachew D. Belew
- PhD Programme in Experimental Biology and Biomedicine, Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal; (A.R.-C.); (G.D.B.)
- Center for Neuroscience and Cell Biology (CNC-UC), Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH 45701, USA
| | - Ivan Viegas
- Centre for Functional Ecology (CFE), TERRA Associate Laboratory, Department of Life Sciences, University of Coimbra, 3030-790 Coimbra, Portugal;
| | - Ludgero C. Tavares
- Vasco da Gama Research Center (CIVG), University School Vasco da Gama, 3020-210 Coimbra, Portugal;
| | - Maria João Meneses
- iNOVA4Health, NOVA Medical School, Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, 1150-082 Lisboa, Portugal; (M.J.M.); (B.P.); (M.P.M.)
| | - Bárbara Patrício
- iNOVA4Health, NOVA Medical School, Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, 1150-082 Lisboa, Portugal; (M.J.M.); (B.P.); (M.P.M.)
- National Research Council (CNR), Institute of Clinical Physiology (IFC), 56124 Pisa, Italy;
- Scuola Superiore Sant’Anna, 56127 Pisa, Italy
| | - Amalia Gastaldelli
- National Research Council (CNR), Institute of Clinical Physiology (IFC), 56124 Pisa, Italy;
- Scuola Superiore Sant’Anna, 56127 Pisa, Italy
| | - Maria Paula Macedo
- iNOVA4Health, NOVA Medical School, Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, 1150-082 Lisboa, Portugal; (M.J.M.); (B.P.); (M.P.M.)
- APDP-Diabetes Portugal Education and Research Center (APDP-ERC), 1250-203 Lisboa, Portugal
| | - John G. Jones
- Center for Neuroscience and Cell Biology (CNC-UC), Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal
- Grupo de Estudos de Investigação Fundamental e Translacional (GIFT) da Sociedade Portuguesa de Diabetologia, 1250-198 Lisboa, Portugal
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Coelho M, Mahar R, Belew GD, Torres A, Barosa C, Cabral F, Viegas I, Gastaldelli A, Mendes VM, Manadas B, Jones JG, Merritt ME. Enrichment of hepatic glycogen and plasma glucose from H₂ 18 O informs gluconeogenic and indirect pathway fluxes in naturally feeding mice. NMR IN BIOMEDICINE 2023; 36:e4837. [PMID: 36151589 PMCID: PMC9845176 DOI: 10.1002/nbm.4837] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 08/22/2022] [Accepted: 09/20/2022] [Indexed: 06/16/2023]
Abstract
Deuterated water (2 H2 O) is a widely used tracer of carbohydrate biosynthesis in both preclinical and clinical settings, but the significant kinetic isotope effects (KIE) of 2 H can distort metabolic information and mediate toxicity. 18 O-water (H2 18 O) has no significant KIE and is incorporated into specific carbohydrate oxygens via well-defined mechanisms, but to date it has not been evaluated in any animal model. Mice were given H2 18 O during overnight feeding and 18 O-enrichments of liver glycogen, triglyceride glycerol (TG), and blood glucose were quantified by 13 C NMR and mass spectrometry (MS). Enrichment of oxygens 5 and 6 relative to body water informed indirect pathway contributions from the Krebs cycle and triose phosphate sources. Compared with mice fed normal chow (NC), mice whose NC was supplemented with a fructose/glucose mix (i.e., a high sugar [HS] diet) had significantly higher indirect pathway contributions from triose phosphate sources, consistent with fructose glycogenesis. Blood glucose and liver TG 18 O-enrichments were quantified by MS. Blood glucose 18 O-enrichment was significantly higher for HS versus NC mice and was consistent with gluconeogenic fructose metabolism. TG 18 O-enrichment was extensive for both NC and HS mice, indicating a high turnover of liver triglyceride, independent of diet. Thus H2 18 O informs hepatic carbohydrate biosynthesis in similar detail to 2 H2 O but without KIE-associated risks.
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Affiliation(s)
- Margarida Coelho
- CNC ‐ Center for Neurosciences and Cell BiologyUniversity of CoimbraCoimbraPortugal
- Department of Chemistry, Faculty of Sciences and TechnologyUniversity of CoimbraCoimbraPortugal
| | - Rohit Mahar
- Department of Biochemistry and Molecular BiologyUniversity of FloridaGainesvilleFloridaUSA
| | - Getachew D. Belew
- CNC ‐ Center for Neurosciences and Cell BiologyUniversity of CoimbraCoimbraPortugal
| | - Alejandra Torres
- CNC ‐ Center for Neurosciences and Cell BiologyUniversity of CoimbraCoimbraPortugal
| | - Cristina Barosa
- CNC ‐ Center for Neurosciences and Cell BiologyUniversity of CoimbraCoimbraPortugal
| | - Fernando Cabral
- CNC ‐ Center for Neurosciences and Cell BiologyUniversity of CoimbraCoimbraPortugal
| | - Ivan Viegas
- Center for Functional Ecology, Department of Life SciencesUniversity of CoimbraCoimbraPortugal
| | | | - Vera M. Mendes
- CNC ‐ Center for Neurosciences and Cell BiologyUniversity of CoimbraCoimbraPortugal
| | - Bruno Manadas
- CNC ‐ Center for Neurosciences and Cell BiologyUniversity of CoimbraCoimbraPortugal
| | - John G. Jones
- CNC ‐ Center for Neurosciences and Cell BiologyUniversity of CoimbraCoimbraPortugal
| | - Matthew E. Merritt
- Department of Biochemistry and Molecular BiologyUniversity of FloridaGainesvilleFloridaUSA
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Viegas I, Di Nunzio G, Belew GD, Torres AN, Silva JG, Perpétuo L, Barosa C, Tavares LC, Jones JG. Integration of Liver Glycogen and Triglyceride NMR Isotopomer Analyses Provides a Comprehensive Coverage of Hepatic Glucose and Fructose Metabolism. Metabolites 2022; 12:1142. [PMID: 36422282 PMCID: PMC9698123 DOI: 10.3390/metabo12111142] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Revised: 11/10/2022] [Accepted: 11/16/2022] [Indexed: 10/18/2023] Open
Abstract
Dietary glucose and fructose are both efficiently assimilated by the liver but a comprehensive measurement of this process starting from their conversion to sugar phosphates, involvement of the pentose phosphate pathway (PPP), and conversion to glycogen and lipid storage products, remains incomplete. Mice were fed a chow diet supplemented with 35 g/100 mL drinking water of a 55/45 fructose/glucose mixture for 18 weeks. On the final night, the sugar mixture was enriched with either [U-13C]glucose or [U-13C]fructose, and deuterated water (2H2O) was also administered. 13C-isotopomers representing newly synthesized hepatic glucose-6-phosphate (glucose-6-P), glycerol-3-phosphate, and lipogenic acetyl-CoA were quantified by 2H and 13C NMR analysis of post-mortem liver glycogen and triglyceride. These data were applied to a metabolic model covering glucose-6-P, PPP, triose-P, and de novo lipogenesis (DNL) fluxes. The glucose supplement was converted to glucose-6-P via the direct pathway, while the fructose supplement was metabolized by the liver to gluconeogenic triose-P via fructokinase-aldolase-triokinase. Glucose-6-P from all carbohydrate sources accounted for 40-60% of lipogenic acetyl-CoA and 10-12% was oxidized by the pentose phosphate pathway (PPP). The yield of NADPH from PPP flux accounted for a minority (~30%) of the total DNL requirement. In conclusion, this approach integrates measurements of glucose-6-P, PPP, and DNL fluxes to provide a holistic and informative assessment of hepatic glucose and fructose metabolism.
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Affiliation(s)
- Ivan Viegas
- Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Coimbra, Portugal
| | - Giada Di Nunzio
- Center for Neurosciences and Cell Biology, University of Coimbra, UC-Biotech, Biocant Park, Nucleo 8, Lote 4, 3060-197 Cantanhede, Portugal
| | - Getachew D. Belew
- Center for Neurosciences and Cell Biology, University of Coimbra, UC-Biotech, Biocant Park, Nucleo 8, Lote 4, 3060-197 Cantanhede, Portugal
- Biotechnology Department, Addis Ababa Science and Technology University, Addis Ababa, Ethiopia
| | - Alejandra N. Torres
- Center for Neurosciences and Cell Biology, University of Coimbra, UC-Biotech, Biocant Park, Nucleo 8, Lote 4, 3060-197 Cantanhede, Portugal
| | - João G. Silva
- Center for Neurosciences and Cell Biology, University of Coimbra, UC-Biotech, Biocant Park, Nucleo 8, Lote 4, 3060-197 Cantanhede, Portugal
| | - Luis Perpétuo
- Center for Neurosciences and Cell Biology, University of Coimbra, UC-Biotech, Biocant Park, Nucleo 8, Lote 4, 3060-197 Cantanhede, Portugal
- iBiMED, Department of Medical Sciences, University of Aveiro, Aveiro, Portugal
| | - Cristina Barosa
- Center for Neurosciences and Cell Biology, University of Coimbra, UC-Biotech, Biocant Park, Nucleo 8, Lote 4, 3060-197 Cantanhede, Portugal
| | - Ludgero C. Tavares
- CIVG—Vasco da Gama Research Center, University School Vasco da Gama—EUVG, 3020-210 Coimbra, Portugal
| | - John G. Jones
- Center for Neurosciences and Cell Biology, University of Coimbra, UC-Biotech, Biocant Park, Nucleo 8, Lote 4, 3060-197 Cantanhede, Portugal
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Barosa C, Ribeiro RT, Andrade R, Raposo JF, Jones JG. Effects of Meal Fructose/Glucose Composition on Postprandial Glucose Appearance and Hepatic Glycogen Synthesis in Healthy Subjects. J Clin Med 2021; 10:jcm10040596. [PMID: 33562492 PMCID: PMC7915433 DOI: 10.3390/jcm10040596] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 01/20/2021] [Accepted: 01/29/2021] [Indexed: 12/31/2022] Open
Abstract
Dietary fructose overshadows glucose in promoting metabolic complications. Intestinal fructose metabolism (IFM) protects against these effects in rodents, by favoring gluconeogenesis, but the extent of IFM in humans is not known. We therefore aimed to infer the extent of IFM by comparing the contribution of dietary fructose to systemic glucose and hepatic glycogen appearance postprandially. Twelve fasting healthy subjects ingested two protein meals in random order, one supplemented with 50 g 5/95 fructose/glucose (LF) and the other with 50 g 55/45 fructose/glucose (HF). Sources of postprandial plasma glucose appearance and hepatic glycogen synthesis were determined with deuterated water. Plasma glucose excursions, as well as pre- and post-meal insulin, c-peptide, and triglyceride levels were nearly identical for both meals. The total gluconeogenic contribution to plasma glucose appearance was significantly higher for HF versus LF (65 ± 2% vs. 34 ± 3%, p < 0.001). For HF, Krebs cycle anaplerosis accounted for two-thirds of total gluconeogenesis (43 ± 2%) with one-third from Triose-P sources (22 ± 1%). With LF, three-quarters of the total gluconeogenic contribution originated via Krebs cycle anaplerosis (26 ± 2%) with one-quarter from Triose-P sources (9 ± 2%). HF and LF gave similar direct and indirect pathway contributions to hepatic glycogen synthesis. Increasing the fructose/glucose ratio had significant effects on glucose appearance sources but no effects on hepatic glycogen synthesis sources, consistent with extensive IFM. The majority of fructose carbons were converted to glucose via the Krebs cycle.
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Affiliation(s)
- Cristina Barosa
- Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal;
| | - Rogério T. Ribeiro
- Education and Research Center, Associação Protetora dos Diabéticos de Portugal (APDP), 1250-189 Lisbon, Portugal; (R.T.R.); (R.A.); (J.F.R.)
| | - Rita Andrade
- Education and Research Center, Associação Protetora dos Diabéticos de Portugal (APDP), 1250-189 Lisbon, Portugal; (R.T.R.); (R.A.); (J.F.R.)
| | - João F. Raposo
- Education and Research Center, Associação Protetora dos Diabéticos de Portugal (APDP), 1250-189 Lisbon, Portugal; (R.T.R.); (R.A.); (J.F.R.)
| | - John G. Jones
- Center for Neuroscience and Cell Biology, University of Coimbra, 3004-504 Coimbra, Portugal;
- Education and Research Center, Associação Protetora dos Diabéticos de Portugal (APDP), 1250-189 Lisbon, Portugal; (R.T.R.); (R.A.); (J.F.R.)
- Correspondence:
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Coelho M, Barosa C, Tavares L, Jones JG. Metabolic incorporation of H 218 O into specific glucose-6-phosphate oxygens by red-blood-cell lysates as observed by 13 C isotope-shifted NMR signals. NMR IN BIOMEDICINE 2020; 33:e4395. [PMID: 32789995 DOI: 10.1002/nbm.4395] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Revised: 07/24/2020] [Accepted: 07/25/2020] [Indexed: 06/11/2023]
Abstract
Water enriched with oxygen-18 (H218 O) is a potential tracer for evaluating the sources of glucose and glycogen synthesis since it is incorporated into specific sites of glucose-6-phosphate via specific enzyme-mediated exchange/addition mechanisms. Unlike 2 H, 18 O does not experience significant isotope effects for any of these processes. Therefore, H218 O might provide more precise estimates of endogenous carbohydrate synthesis compared with deuterated water provided that positional 18 O enrichments of glucose can be measured. As a proof of concept, H218 O was incorporated into a well characterized hemolysate model of sugar phosphate metabolism and 13 C NMR was applied to quantify positional 18 O enrichment of glucose-6-phosphate oxygens. Human erythrocyte hemolysate preparations were incubated overnight at 37 °C with a buffer containing sugar phosphate precursors and 20% (n = 5) and 80% (n = 1) H218 O. Enrichment of glucose-6-phosphate was analyzed by 13 C NMR analysis of 18 O-shifted versus unshifted signals following derivatization to monoacetone glucose (MAG). 13 C NMR MAG spectra from hemolysate revealed resolved 18 O-shifted signals in Positions 1-5. Mean 18 O enrichments were 16.4 ± 1.6% (Position 1), 13.3 ± 1.3% (Position 2), 4.1 ± 1.1% (Position 3), 12.6 ± 0.8% (Position 4), 10.7 ± 1.4% (Position 5), and no detectable enrichment of Position 6. No 18 O-shifted glucose-6-phosphate signals were detected in preparations containing sugar phosphate precursors only. H218 O is incorporated into Positions 1-5 of glucose-6-phosphate in accordance with spontaneous aldose hydration and specific enzymatic reaction mechanisms. This provides a basis for its deployment as a tracer for glucose and glycogen biosynthesis.
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Affiliation(s)
- Margarida Coelho
- Center for Neurosciences and Cell Biology, University of Coimbra, Portugal
- Chemistry Department, Faculty of Sciences and Technology, University of Coimbra, Portugal
| | - Cristina Barosa
- Center for Neurosciences and Cell Biology, University of Coimbra, Portugal
| | - Ludgero Tavares
- Center for Neurosciences and Cell Biology, University of Coimbra, Portugal
| | - John G Jones
- Center for Neurosciences and Cell Biology, University of Coimbra, Portugal
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S-Nitrosoglutathione Reverts Dietary Sucrose-Induced Insulin Resistance. Antioxidants (Basel) 2020; 9:antiox9090870. [PMID: 32942712 PMCID: PMC7555592 DOI: 10.3390/antiox9090870] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 09/08/2020] [Accepted: 09/09/2020] [Indexed: 02/06/2023] Open
Abstract
The liver is a fundamental organ to ensure whole-body homeostasis, allowing for a proper increase in insulin sensitivity from the fast to the postprandial status. Hepatic regulation of glucose metabolism is crucial and has been shown to be modulated by glutathione (GSH) and nitric oxide (NO). However, knowledge of the metabolic action of GSH and NO in glucose homeostasis remains incomplete. The current study was designed to test the hypothesis that treatment with S-nitrosoglutathione is sufficient to revert insulin resistance induced by a high-sucrose diet. Male Wistar rats were divided in a control or high-sucrose group. Insulin sensitivity was determined: (i) in the fast state; (ii) after a standardized test meal; (iii) after GSH + NO; and after (iv) S-nitrosoglutathione (GSNO) administration. The fasting glucose level was not different between the control and high-sucrose group. In the liver, the high-sucrose model shows increased NO and unchanged GSH levels. In control animals, insulin sensitivity increased after a meal or administration of GSH+NO/GSNO, but this was abrogated by sucrose feeding. GSNO was able to revert insulin resistance induced by sucrose feeding, in a dose-dependent manner, suggesting that they have an insulin-sensitizing effect in vivo. These effects are associated with an increased insulin receptor and Akt phosphorylation in muscle cells. Our findings demonstrate that GSNO promotes insulin sensitivity in a sucrose-induced insulin-resistant animal model and further implicates that this antioxidant molecule may act as a potential pharmacological tool for the treatment of insulin resistance in obesity and type 2 diabetes.
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Determining the contribution of a high-fructose corn syrup formulation to hepatic glycogen synthesis during ad-libitum feeding in mice. Sci Rep 2020; 10:12852. [PMID: 32733017 PMCID: PMC7393509 DOI: 10.1038/s41598-020-69820-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Accepted: 07/06/2020] [Indexed: 11/28/2022] Open
Abstract
Excessive sugar intake including high-fructose corn syrup (HFCS) is implicated in the rise of obesity, insulin resistance and non-alcoholic fatty liver disease. Liver glycogen synthesis is influenced by both fructose and insulin signaling. Therefore, the effect of HFCS on hepatic glycogenesis was evaluated in mice feeding ad-libitum. Using deuterated water: the fraction of glycogen derived from triose-P sources, Krebs cycle substrates, and direct pathway + cycling, was measured in 9 normal-chow fed mice (NC) and 12 mice fed normal chow plus a 55% fructose/45% glucose mix in the drinking water at 30% w/v (HFCS-55). This was enriched with [U-13C]fructose or [U-13C]glucose to determine the contribution of each to glycogenesis. For NC, direct pathway + cycling, Krebs cycle, and triose-P sources accounted for 66 ± 0.7%, 23 ± 0.8% and 11 ± 0.4% of glycogen synthesis, respectively. HFCS-55 mice had similar direct pathway + cycling (64 ± 1%) but lower Krebs cycle (12 ± 1%, p < 0.001) and higher triose-P contributions (24 ± 1%, p < 0.001). HFCS-55-fructose contributed 17 ± 1% via triose-P and 2 ± 0% via Krebs cycle. HFCS-55-glucose contributed 16 ± 3% via direct pathway and 1 ± 0% via Krebs cycle. In conclusion, HFCS-55 supplementation resulted in similar hepatic glycogen deposition rates. Indirect pathway contributions shifted from Krebs cycle to Triose-P sources reflecting HFCS-55-fructose utilization, while HFCS-55-glucose was incorporated almost exclusively by the direct pathway.
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Role of phosphorylation on characteristics of glycogen phosphorylase in lamb with different glycolytic rates post-mortem. Meat Sci 2020; 164:108096. [PMID: 32145602 DOI: 10.1016/j.meatsci.2020.108096] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 02/24/2020] [Indexed: 01/22/2023]
Abstract
The relationship between glycogen phosphorylase activity and phosphorylation levels in the longissimus thoracis muscle post-mortem was studied. Sixty lamb samples were collected at 0.5 h, 2 h, 6 h, 12 h, 24 h, 48 h, and 72 h post-mortem and divided into three groups (n = 6) with different glycolytic rates (fast, intermediate, and slow) according to the pH at 6 h post-mortem. The phosphorylation level and activity and expression of glycogen phosphorylase were determined. The results showed that the phosphorylation level and activity of glycogen phosphorylase in the slow pH decline group was lower than that in the fast pH decline group during 24 h post-mortem (P < .05). There was a significant positive correlation between the glycogen phosphorylase activity and the phosphorylation level. In conclusion, these data demonstrated that the glycogen phosphorylase activity in lambs was affected by phosphorylation levels and postmortem duration.
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