A threshold exists for the stimulatory effect of insulin on plasma l-carnitine clearance in humans
Abstract
Maintaining hyperinsulinemia ( approximately 160 mU/l) during steady-state hypercarnitinemia ( approximately 550 mumol/l) increases skeletal muscle total carnitine (TC) content by approximately 15% within 5 h. The aim of the present study was to further examine the relationship between serum insulin concentration and skeletal muscle carnitine accumulation by attempting to identify the serum insulin concentration at which this stimulatory effect of insulin on carnitine retention becomes apparent. On four randomized experimental visits, eight healthy men (body mass index 23.8 +/- 0.9 kg/m(2)) underwent a 6-h euglycemic insulin clamp of 5, 30, 55, or 105 mU x m(-2) x min(-1) accompanied by a 5-h iv infusion of l-carnitine (15 mg/kg bolus followed by 10 mg x kg(-1) x h(-1)). The clamps produced steady-state serum insulin concentrations of 10.1 +/- 0.5, 48.8 +/- 1.0, 88.9 +/- 2.8, and 173.9 +/- 6.5 mU/l, respectively. During l-carnitine infusion, plasma TC concentration remained above 450 mumol/l during all four visits. However, there was a significant treatment effect of insulin (P < 0.001), such that by the end of infusion the plasma TC concentration in the 55- and 105-mU clamps was lower than that seen in the 5- (P < 0.05 and P < 0.01, respectively) and 30-mU (P < 0.01) clamps. The findings demonstrate that only high circulating serum insulin concentrations (> or =90 mU/l) are capable of stimulating skeletal muscle carnitine accumulation. This is of relevance to athletes, and the treatment of obesity and type 2 diabetes, where increasing skeletal muscle carnitine content may be used as tool to modify skeletal muscle energy metabolism.
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Hyperinsulinemia (>50 mU/L) promotes carnitine uptake into skeletal muscle.
“However, hyperinsulinemia (>50 mU/L) promotes carnitine uptake into skeletal muscle [192,193]”
From Nutritional Considerations for the Vegan Athlete (2023) · cites this paper as [193]
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Skeletal muscle energy metabolism during exercise
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Self-citation
- Authors
- Stephens, F. B., Constantin-Teodosiu, D., Laithwaite, D., Simpson, E. J., & Greenhaff, P. L.
- Affiliations
- University of Nottingham (GB)
- Venue
- American Journal of Physiology-Endocrinology and Metabolism
- Publisher
- American Physiological Society
- Published
- 2007-02
- Volume
- 292
- Issue
- 2
- Pages
- E637-E641
- ISSN
- 0193-1849 (ISSN-L)
- 1522-1555
- OpenAlex
- W2128477744
- Cited by
- 23
- References
- 33
- Citations by year
- 2026: 1 · 2025: 2 · 2024: 1 · 2023: 3 · 2021: 1 · 2020: 1 · 2018: 1 · 2017: 1 · 2016: 1 · 2015: 1 · 2013: 2 · 2012: 2
- FWCI
- 0.55
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- American Journal of Physiology-Endocrinology and Metabolism (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Muscle metabolism and nutrition
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Metabolism, Diabetes, and Cancer
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Clinical Biochemistry › Metabolism and Genetic Disorders
- Keywords
- insulin, L-carnitine, hyperinsulinemia, hyperinsulinemic-euglycemic clamp, skeletal muscle energy metabolism, obesity, type 2 diabetes
- MeSH terms
- Adult, Carnitine, Humans, Infusion Pumps, Insulin, Male, Muscle, Skeletal
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