Effects of NK1 receptors on gastric motor functions and satiation in healthy humans: results from a controlled trial with the NK1 antagonist aprepitant

Aprepitant, an NK1 receptor antagonist, is approved for the treatment of chemotherapy-induced or postoperative emesis by blocking NK1 receptors in the brain stem vomiting center. The effects of NK1 receptors on gastric functions and postprandial symptoms in humans are unclear; a single, crossover study did not show a significant effect of aprepitant on gastrointestinal transit. Our aim was to compare, in a randomized, double-blind, placebo-controlled, parallel-group study (12 healthy volunteers per group), the effects of aprepitant vs. placebo on gastric emptying of solids (by scintigraphy) with a 320-kcal meal, gastric volumes (GVs; fasting and accommodation by single photon emission-computed tomography), satiation [maximum tolerated volume (MTV)], and symptoms after a dyspeptogenic meal of Ensure. Aprepitant (125 mg on day 1, followed by 80 mg on days 2-5) or placebo, one tablet daily, was administered for 5 consecutive days. Statistical analysis was by unpaired rank sum test, adjusted for sex difference and body mass index. To assess treatment effects on symptoms, we incorporated MTV in the model. Aprepitant increased fasting, postprandial, and accommodation GV and tended to increase volume to fullness and MTV by similar to 200 kcal. However, aprepitant increased aggregate symptoms, nausea, and pain scores after ingestion the MTV of Ensure. There was no significant effect of aprepitant on gastric half-emptying time of solids. We conclude that NK1 receptors are involved in the control of GV and in determining postprandial satiation and symptoms. Further studies of the pharmacodynamics and therapeutic role of NK1 receptor antagonists in patients with gastroparesis and dyspepsia are warranted. NEW & NOTEWORTHY Aprepitant increases fasting, postprandial, and accommodation gastric volumes. Aprepitant increases volume to fullness and maximum tolerated volume during a nutrient drink test. NK1 receptors are involved in the control of gastric volume and in determining postprandial satiation and symptoms.