Correlation Between Gastric Emptying and Gastric Adaptive Relaxation Influenced by Amino Acids

Abstract

Background/aims: Amino acids have many physiological activities. We report the correlation between gastric emptying and gastric adaptive relaxation using tryptophan and amino acids with a straight alkyl chain, hydroxylated chain, and branched chain. Here we sought to further clarify the correlation between gastric emptying and gastric adaptive relaxation by using other amino acids.

Methods: In Sprague-Dawley rats, gastric emptying was evaluated by a breath test using [1-¹³C] acetic acid. The expired ¹³CO₂ pattern, T_max, C_max, and AUC_120min values were used as evaluation items. Gastric adaptive relaxation was evaluated in a barostat experiment. Individual amino acids (1 g/kg) were administered orally 30 minutes before each breath test or barostat test.

Results: L-phenylalanine and L-tyrosine did not influence gastric emptying. All other amino acids, ie, L-proline, L-histidine, L-cysteine, L-methionine, L-aspartic acid, L-glutamic acid, L-asparagine, L-arginine, L-glutamine, and L-lysine significantly delayed and inhibited gastric emptying. L-Cysteine and L-aspartic acid significantly enhanced and L-methionine and L-glutamine significantly inhibited gastric adaptive relaxation. L-Phenylalanine moved the balloon toward the antrum, suggesting strong contraction of the fundus. T_max showed a significant positive correlation (r = 0.709), and C_max and AUC_120min each showed negative correlations (r = 0.613 and 0.667, respectively) with gastric adaptive relaxation.

Conclusion: From the above findings, it was found that a close correlation exists between gastric emptying and adaptive relaxation, suggesting that enhanced gastric adaptive relaxation inhibits gastric emptying.

Keywords: Amino acids; Aspartic acid; Gastric emptying; Phenylalanine; Rats.

Figure 1

The effects of L-proline, L-histidine, L-tyrosine, L-phenylalanine, L-cysteine, and L-methionine on gastric emptying (A) and gastric adaptive relaxation (B) in rats. Values are mean ± SEM (n = 4 in gastric emptying and n = 6 in gastric adaptive relaxation). P-values represent the difference from controls. NE means not evaluated, because L-phenylalanine moved the balloon toward the antrum from the fundus in all rats used (n = 6).

Figure 2

The effects of L-aspartic acid, L-glutamic acid, L-asparagine, L-arginine, L-glutamine, and L-lysine on the gastric emptying (A) and gastric adaptive relaxation (B) in rats. Values are mean ± SEM (n = 4 in gastric emptying and n = 6 in gastric adaptive relaxation). P-values represent the difference from controls.

Figure 3

The correlations between gastric adaptive relaxation and gastric emptying parameters T_max, C_max, and AUC_120min in rats. By adding T_max, C_max or AUC_120min values and gastric adaptive relaxation from references , , and to the present results, a significant positive correlation was obtained between T_max values and gastric adaptive relaxation (A; r = 0.709 P < 0.01). Moreover, significant negative correlations were obtained between C_max values and gastric adaptive relaxation (B; r = 0.613 P < 0.01) and between AUC_120min values and gastric adaptive relaxation (C; r = 0.667 P < 0.01). Open circles are the control values.

Figure 4

The chemical structures of the amino acids and their effects on the gastric emptying and gastric adaptive relaxation. NE means not evaluated, because L-phenylalanine moved the balloon toward the antrum from the fundus in all rats used (n = 6).