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Nutrition and Supplements
L-Citrulline Supports Vascular and Muscular Benefits of Exercise Training in Older Adults
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<blockquote data-quote="madman" data-source="post: 181473" data-attributes="member: 13851"><p>Only take l-citrulline 6 grams (3 grams twice daily).</p><p></p><p>Aim for a minimum of 3 grams daily but 6 would be more effective overall.</p><p></p><p>L-arginine is not needed.</p><p></p><p></p><p></p><p></p><p><strong>L-CIT and Vascular Function </strong></p><p></p><p><em><span style="color: rgb(184, 49, 47)"><strong>Evidence indicates that even though oral L-ARG supplementation effectively increases L-ARG bioavailability, improvement in endothelial-mediated vasodilation is not observed in healthy middle-aged adults (20).</strong></span></em> <em><strong><span style="color: rgb(184, 49, 47)">Long-term L-ARG supplementation becomes ineffective due to increased catabolism by arginase enzyme activation (19).</span></strong></em> <span style="color: rgb(44, 130, 201)"><em><strong>Alternatively, the nonessential amino acid L-CIT is better absorbed when ingested as compared with a similar dose of oral L-ARG (19). The higher circulating level of L-ARG after L-CIT ingestion is the result of lack of catabolism by arginase and hepatic uptake (19). Part of this efficiency is attributed to the ability of L-CIT to inhibit arginase activity in humans and animals (11,21).</strong></em></span> <em><strong><span style="color: rgb(44, 130, 201)">Circulating L-CIT is converted to L-ARG (de novo synthesis) and released from the kidneys into the systemic circulation (22). </span></strong></em>The greater efficacy of acute oral L-CIT as a precursor of plasma L-ARG than an equimolar dose of oral L-ARG was demonstrated by Moinard et al. (9) in older adults. <span style="color: rgb(0, 0, 0)">We have shown increases in plasma L-ARG or NO metabolites after 1 wk (7), 2 wk (23), and 8 wk (14) of oral L-CIT in older adults. Therefore, L-CIT supplementation may have the potential to improve age-related vascular dysfunction by increasing L-ARG bioavailability for eNOS via de novo synthesis and arginase inhibition. </span></p><p></p><p></p><p></p><p><span style="color: rgb(184, 49, 47)"><strong><em>L-CIT combined with L-ARG may have additive effects.</em></strong></span><span style="color: rgb(0, 0, 0)"> We found that oral supplementation with L-CIT and L-ARG caused a greater increase in plasma L-ARG, NO metabolites, and cGMP levels than the single amino acid alone in animals (21). These effects of L-CIT plus L-ARG were associated with enhanced peripheral blood flow. The upregulation of the L-ARG‐NO‐cGMP pathway by the combined amino acid supplementation was likely via the effect of L-CIT on arginase activity, acting as a strong allosteric inhibitor (19). </span><span style="color: rgb(184, 49, 47)"><em><strong>To test for the clinical and applied utility of this combined supplementation, Suzukiet al.(35) assessed performance on a bicycle ergometer in male athletes and demonstrated that 7 d of oral L-CIT (1.2 g·d-1) and L-ARG (1.2 g·d-1) improved 10-min fullpower cycling test performance and postexercise subjective perception related to muscle fatigue. <u>Although the L-CIT plus L-ARG combination may provide superior efficacy leading to cardiovascular benefits by promoting greater L-ARG‐NO‐cGMP bioavailability than each amino acid alone, further studies are needed to elucidate the effectiveness on exercise performance or tolerance in older adults and clinical populations</u>. </strong></em></span><span style="color: rgb(44, 130, 201)"><strong><em>These findings suggest that L-CIT improves local muscle oxygen kinetics and cycling performance despite no changes in oxygen consumption, likely due to enhanced microvascular function and reduced ammonia accumulation. <u>These effects may be more pronounced when combining L-CIT and L-ARG</u>. </em></strong></span></p></blockquote><p></p>
[QUOTE="madman, post: 181473, member: 13851"] Only take l-citrulline 6 grams (3 grams twice daily). Aim for a minimum of 3 grams daily but 6 would be more effective overall. L-arginine is not needed. [B]L-CIT and Vascular Function [/B] [I][COLOR=rgb(184, 49, 47)][B]Evidence indicates that even though oral L-ARG supplementation effectively increases L-ARG bioavailability, improvement in endothelial-mediated vasodilation is not observed in healthy middle-aged adults (20).[/B][/COLOR][/I][B] [/B][I][B][COLOR=rgb(184, 49, 47)]Long-term L-ARG supplementation becomes ineffective due to increased catabolism by arginase enzyme activation (19).[/COLOR][/B][/I] [COLOR=rgb(44, 130, 201)][I][B]Alternatively, the nonessential amino acid L-CIT is better absorbed when ingested as compared with a similar dose of oral L-ARG (19). The higher circulating level of L-ARG after L-CIT ingestion is the result of lack of catabolism by arginase and hepatic uptake (19). Part of this efficiency is attributed to the ability of L-CIT to inhibit arginase activity in humans and animals (11,21).[/B][/I][/COLOR] [I][B][COLOR=rgb(44, 130, 201)]Circulating L-CIT is converted to L-ARG (de novo synthesis) and released from the kidneys into the systemic circulation (22). [/COLOR][/B][/I]The greater efficacy of acute oral L-CIT as a precursor of plasma L-ARG than an equimolar dose of oral L-ARG was demonstrated by Moinard et al. (9) in older adults. [COLOR=rgb(0, 0, 0)]We have shown increases in plasma L-ARG or NO metabolites after 1 wk (7), 2 wk (23), and 8 wk (14) of oral L-CIT in older adults. Therefore, L-CIT supplementation may have the potential to improve age-related vascular dysfunction by increasing L-ARG bioavailability for eNOS via de novo synthesis and arginase inhibition. [/COLOR] [COLOR=rgb(184, 49, 47)][B][I]L-CIT combined with L-ARG may have additive effects.[/I][/B][/COLOR][COLOR=rgb(0, 0, 0)] We found that oral supplementation with L-CIT and L-ARG caused a greater increase in plasma L-ARG, NO metabolites, and cGMP levels than the single amino acid alone in animals (21). These effects of L-CIT plus L-ARG were associated with enhanced peripheral blood flow. The upregulation of the L-ARG‐NO‐cGMP pathway by the combined amino acid supplementation was likely via the effect of L-CIT on arginase activity, acting as a strong allosteric inhibitor (19). [/COLOR][COLOR=rgb(184, 49, 47)][I][B]To test for the clinical and applied utility of this combined supplementation, Suzukiet al.(35) assessed performance on a bicycle ergometer in male athletes and demonstrated that 7 d of oral L-CIT (1.2 g·d-1) and L-ARG (1.2 g·d-1) improved 10-min fullpower cycling test performance and postexercise subjective perception related to muscle fatigue. [U]Although the L-CIT plus L-ARG combination may provide superior efficacy leading to cardiovascular benefits by promoting greater L-ARG‐NO‐cGMP bioavailability than each amino acid alone, further studies are needed to elucidate the effectiveness on exercise performance or tolerance in older adults and clinical populations[/U]. [/B][/I][/COLOR][COLOR=rgb(44, 130, 201)][B][I]These findings suggest that L-CIT improves local muscle oxygen kinetics and cycling performance despite no changes in oxygen consumption, likely due to enhanced microvascular function and reduced ammonia accumulation. [U]These effects may be more pronounced when combining L-CIT and L-ARG[/U]. [/I][/B][/COLOR][COLOR=rgb(0, 0, 0)][/COLOR] [/QUOTE]
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L-Citrulline Supports Vascular and Muscular Benefits of Exercise Training in Older Adults
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