Effect of L-Glutamine on Chylomicron Formation and Fat-Induced Activation of Intestinal Mucosal Mast Cells in Sprague-Dawley Rats

Abstract

Glutamine (Gln) is required for intestinal mucosal homeostasis, and it can promote triglyceride absorption. The intestinal mucosal mast cells (MMCs) are activated during fat absorption. This study investigated the potential role of Gln on fat absorption-induced activation of MMCs in rats. Lymph fistula rats (n = 24) were studied after an overnight recovery with the infusion of saline only, saline plus 85 mM L-glutamine (L-Gln) or 85 mM D-glutamine (D-Gln), respectively. On the test day, rats (n = 8/group) were given an intraduodenal bolus of 20% Intralipid contained either saline only (vehicle group), 85 mM L-Gln (L-Gln group), or 85 mM D-Gln (D-Gln group). Lymph was collected hourly for up to 6 h for analyses. The results showed that intestinal lymph from rats given L-Gln had increased levels of apolipoprotein B (ApoB) and A-I (ApoA-I), concomitant with an increased spectrum of smaller chylomicron particles. Unexpectedly, L-Gln also increased levels of rat mucosal mast cell protease II (RMCPII), as well as histamine and prostaglandin D₂ (PGD₂) in response to dietary lipid. However, these effects were not observed in rats treated with 85 mM of the stereoisomer D-Gln. Our results showed that L-glutamine could specifically activate MMCs to degranulate and release MMC mediators to the lymph during fat absorption. This observation is potentially important clinically since L-glutamine is often used to promote gut health and repair leaky gut.

Keywords: L-glutamine; apolipoproteins; intestinal lymph; intestinal mucosal mast cell; lipid.

Figure 1

The lymph flow rate in lymph fistula rats infused intraduodenally with a bolus of 20% Intralipid containing either saline alone (vehicle group), 85 mM L-glutamine (L-Gln group) or 85 mM D-glutamine (D-Gln group), respectively. Data are expressed as mean ± SEM, n = eight per group. * p < 0.05 vehicle vs. D-Gln. L-Gln, L-glutamine; D-Gln, D-glutamine.

Figure 2

Comparison of lymphatic protein output in lymph fistula rats infused intraduodenally with a bolus of 20% Intralipid containing either saline alone (vehicle group), 85 mM L-glutamine (L-Gln group) or 85 mM D-glutamine (D-Gln group), respectively. Data are expressed as mean ± SEM, n = eight per group. L-Gln, L-glutamine; D-Gln, D-glutamine.

Figure 3

The lymphatic outputs of triglycerides in lymph fistula rats infused intraduodenally with a bolus of 20% Intralipid containing either saline alone (vehicle group), 85 mM L-glutamine (L-Gln group) or 85 mM D-glutamine (D-Gln group), respectively. Data are expressed as mean ± SEM, n = eight per group. L-Gln, L-glutamine; D-Gln, D-glutamine.

Figure 4

The lymphatic outputs of phospholipids in lymph fistula rats infused intraduodenally with a bolus of 20% Intralipid containing either saline alone (vehicle group), 85 mM L-glutamine (L-Gln group) or 85 mM D-glutamine (D-Gln group), respectively. Data are expressed as mean ± SEM, n = eight per group. * p < 0.05 D-Gln vs. L-Gln. L-Gln, L-glutamine; D-Gln, D-glutamine.

Figure 5

The lymphatic outputs of ApoB (A), ApoA-I (B), and ApoA-IV (C) in lymph fistula rats infused intraduodenally with a bolus of 20% Intralipid containing either saline alone (vehicle group), 85 mM L-glutamine (L-Gln group) or 85 mM D-glutamine (D-Gln group), respectively. Data are expressed as mean ± SEM, n = eight per group. * p < 0.05, ** p < 0.01 L-Gln vs. vehicle; ## p < 0.01 L-Gln vs. D-Gln. ApoB, Apolipoprotein B; ApoA-I, Apolipoprotein A-I; ApoA-IV, Apolipoprotein A-IV; L-Gln, L-glutamine; D-Gln, D-glutamine.

Figure 6

The analysis of lipoproteins from lymph collected 1 h after a bolus infusion of 20% Intralipid containing either saline alone (vehicle group) or 85 mM L-glutamine (L-Gln group), respectively. Representative electron microscopic images of the lipoprotein particles from vehicle controls (A) and L-Gln-treated rat (B). Scale bar: 200 nm. The size of lipoprotein particles was quantified and the distribution of particle sizes was shown (C). Data are expressed as mean ± SEM, n = eight per group. * p < 0.05 L-Gln vs. vehicle. L-Gln, L-glutamine; D-Gln, D-glutamine.

Figure 7

Lymphatic RMCPII output in lymph fistula rats infused intraduodenally with a bolus of 20% Intralipid containing either saline alone (vehicle group), 85 mM L-glutamine (L-Gln group) or 85 mM D-glutamine (D-Gln group), respectively (A–C) representative Western bolt image showing RMCPII in lymph. C: Calculated areas under the curve for the curves depicting lymphatic RMCPII output. Data are expressed as mean ± SEM, n = eight per group. * p < 0.05, ** p < 0.01 L-Gln vs. vehicle; # p < 0.05, ## p < 0.01 L-Gln vs. D-Gln. RMCPII, rat mucosal mast cell protease II; L-Gln, L-glutamine; D-Gln, D-glutamine.

Figure 8

The lymphatic concentrations of histamine in lymph fistula rats infused intraduodenally with a bolus of 20% Intralipid containing either saline alone (vehicle group), 85 mM L-glutamine (L-Gln group) or 85 mM D-glutamine (D-Gln group), respectively. Data are expressed as mean ± SEM, n = eight per group. * p < 0.05 L-Gln vs. vehicle; ## p < 0.01 L-Gln vs. D-Gln. L-Gln, L-glutamine; D-Gln, D-glutamine.

Figure 9

The lymphatic concentrations of PGD₂ in lymph fistula rats infused intraduodenally with a bolus of 20% Intralipid containing either saline alone (vehicle group), 85 mM L-glutamine (L-Gln group) or 85 mM D-glutamine (D-Gln group), respectively (A). (B): Calculated areas under the curve for the curves depicting the lymphatic concentration of PGD₂. Data are expressed as mean ± SEM, n = eight per group. ** p < 0.01 L-Gln vs. vehicle; # p < 0.05, ## p < 0.01 L-Gln vs. D-Gln; & p < 0.05 vehicle vs. D-Gln. PGD₂, prostaglandin D₂; L-Gln, L-glutamine; D-Gln, D-glutamine.