Evidence for a lipid specific effect in nutrient induced human proximal gastric relaxation

Abstract

Background/aim: The presence of lipid in the upper gut is able to modify gastrointestinal motor performance, but its influence on the relaxation of the human stomach, which is known to modify gastric emptying, remains incompletely understood. The relaxation of the proximal stomach in response to various lipid concentrations was therefore studied in healthy volunteers. Since the observed effects could be mediated through osmolality or energy sensitive pathways, the effects of equicaloric and equiosmolar non-lipid solutions were also determined.

Methods: The tone of the proximal stomach was measured during stepwise inflation of a non-compliant bag sited in the proximal stomach, both before and after a test meal was delivered intragastrically. Iso-osmolar lipid emulsions were diluted in iso-osmolar saline at concentrations of 1.25, 2.5, 5, 10, and 20%. NaCl solutions at osmolalities of 300, 600, 1200 and 2400 mmol/kg and glucose solutions of 836 and 3344 kJ/l were also given.

Results: All lipid meals of 2.5% or greater concentration induced a reduction in gastric tone in a non-dose-dependent manner, responses to 5% lipid (median (range) 74 (62-92)%) being similar to those to 20% lipid (80 (55-83)%; p > 0.05). No relaxation was elicited by isocaloric glucose. NaCl only consistently caused relaxation at 2400 mmol/kg.

Conclusion: Lipid meals reduce human proximal gastric tone by a lipid specific mechanism, independently of their energy content or osmolality.

Figure 1

Effects of representative test meals on intragastric balloon pressure with increasing distension volumes are shown. Values are mean (SEM). A downward shift of the post-meal curve is indicative of a fall in proximal gastric tone. Hence the 1.25% lipid meal (A) had no effect, while 10% lipid (B) was associated with a fall in proximal gastric tone (p<0.05). A 2400 mmol/kg saline solution (C) was also associated with gastric relaxation (p<0.05), while 10% glucose (1200 mmol/kg) (D), which is equivalent to 8% lipid in its energy content, had no significant effect.

Figure 2

Plots showing the effect of the test meals on gastric tone. Results are median + range. Data shown are for n = 6 subjects in all cases except for 2.5% lipid where n = 7. The effect of each test meal is expressed as the percentage of the fasting value (fasting = 100%). (A) The meals containing 2.5-20% lipid all caused significant fundal relaxation (p<0.05 for the difference in values obtained before and after the test meal) but the magnitude of this effect did not increase with increasing lipid concentration above 2.5%. No effect was found for 1.25% lipid. (B) Neither glucose meal caused fundal relaxation (p>0.05 for the difference between values obtained before and after the test meal). The caloric value of 1200 mmol/kg glucose is equivalent to 8% lipid. (C) Significant gastric relaxation was observed only after the 2400 mmol/kg meal (p<0.05 for the difference between values obtained before and after the test meal).