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      Study on the Hyperglycemic Effect of GLP-1 in Spinibarbus denticulatus by Oral Administration and Intraperitoneal Injection Methods


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          Glucagon-like peptide-1 (GLP-1), one of the expression products of the proglucagon (pg) gene, is an incretin mainly secreted by the gastrointestinal system. In mammals, GLP-1 has hypoglycemic and food-inhibiting effects; while in some fish species, it has been confirmed to increase blood glucose by promoting gluconeogenesis and stimulating glycogenolysis. In order to more deeply understand the role of GLP-1 in the process of glycometabolism in herbivorous fish, the pg gene was cloned from Spinibarbus denticulatus to obtain its sequence characteristics, and the changes in blood glucose level and pg gene expression in S. denticulatus were further explored by feeding with three kinds of carbohydrates and intraperitoneal injection of GLP-1. Basal and temporal blood glucose levels and pg gene expression of S. denticulatus (91.68 ± 10.79 g) were measured at 0, 1, 3, 5, 7, and 12 h after oral administration ( n = 4). Then, the changes of blood glucose levels and pg and glucokinase (gk) gene expressions of S. denticulatus (94.29 ± 10.82 g) were determined at 0, 30, 60, and 120 min after intraperitoneal injection ( n = 4). It was shown that polysaccharides could induce the upregulation of pg gene expression faster than monosaccharides and stimulate the secretion of GLP-1 in the intestine. Intraperitoneal injection of GLP-1 peptide rapidly raised blood glucose levels, and pg gene expression in the anterior intestine, whole brain, and hepatopancreas decreased continuously after 30 minutes. These results showed that S. denticulatus might inhibit the excessive accumulation of blood glucose by reducing the expression of the pg gene and increasing the expression of gk gene in a short time. It was speculated that GLP-1 of S. denticulatus might have a “gut-brain-liver” pathway similar to mammals in glycemia regulation. Therefore, this study provided a novel perspective for explaining the functional differences of GLP-1 in herbivorous fish and mammals.

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          Glucose metabolism in fish: a review.

          Teleost fishes represent a highly diverse group consisting of more than 20,000 species living across all aquatic environments. This group has significant economical, societal and environmental impacts, yet research efforts have concentrated primarily on salmonid and cyprinid species. This review examines carbohydrate/glucose metabolism and its regulation in these model species including the role of hormones and diet. Over the past decade, molecular tools have been used to address some of the downstream components of these processes and these are incorporated to better understand the roles played by carbohydrates and their regulatory paths. Glucose metabolism remains a contentious area as many fish species are traditionally considered glucose intolerant and, therefore, one might expect that the use and storage of glucose would be considered of minor importance. However, the actual picture is not so clear since the apparent intolerance of fish to carbohydrates is not evident in herbivorous and omnivorous species and even in carnivorous species, glucose is important for specific tissues and/or for specific activities. Thus, our aim is to up-date carbohydrate metabolism in fish, placing it to the context of these new experimental tools and its relationship to dietary intake. Finally, we suggest that new research directions ultimately will lead to a better understanding of these processes.
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            Utilization of dietary carbohydrate by fish

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              Nutritional regulation of hepatic glucose metabolism in fish.

              Glucose plays a key role as energy source in the majority of mammals, but its importance in fish appears limited. Until now, the physiological basis for such apparent glucose intolerance in fish has not been fully understood. A distinct regulation of hepatic glucose utilization (glycolysis) and production (gluconeogenesis) may be advanced to explain the relative inability of fish to efficiently utilize dietary glucose. We summarize here information regarding the nutritional regulation of key enzymes involved in glycolysis (hexokinases, 6-phosphofructo-1-kinase and pyruvate kinase) and gluconeogenesis (phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase and glucose-6-phosphatase) pathways as well as that of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. The effect of dietary carbohydrate level and source on the activities and gene expression of the mentioned key enzymes is also discussed. Overall, data strongly suggest that the liver of most fish species is apparently capable of regulating glucose storage. The persistent high level of endogenous glucose production independent of carbohydrate intake level may lead to a putative competition between exogenous (dietary) glucose and endogenous glucose as the source of energy, which may explain the poor dietary carbohydrate utilization in fish.

                Author and article information

                Aquac Nutr
                Aquac Nutr
                Aquaculture Nutrition
                3 April 2023
                : 2023
                : 9969406
                1College of Animal Science and Technology, Sichuan Agricultural University, Wenjiang, Chengdu, Sichuan, China
                2Mianyang Academy of Agricultural Sciences, Mianyang, Sichuan, China
                3The Original Stock Farm of Leiocassis longirostris of Sichuan Province, Chongzhou, Sichuan, China
                4Agricultural and Rural Bureau of Chongzhou, Chongzhou, Sichuan, China
                Author notes

                Academic Editor: Sobhan R. Akhavan

                Author information
                Copyright © 2023 Wei Luo et al.

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                : 15 January 2023
                : 14 March 2023
                : 21 March 2023
                Funded by: Sichuan Province Science and Technology Support Program
                Award ID: 2021YFYZ0015
                Funded by: National Natural Science Foundation of China
                Award ID: 32172998
                Research Article


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