Meglumine diatrizoate

Mice were anesthetized through an i.p. injection of Ketamine (80 mg/kg; Ceva, USA). Human IgE stimulation was performed by s.c. injecting human IgE mAb (60 ng/mouse; Calbiochem, USA) at the base of the ear. Twenty‐four hours after sensitization, mice were injected IV with 50 µL of 12.5 mg/mL Evans blue (Sigma–Aldrich). After 10 min, mice were i.p. injected with anti‐human IgE (50 µg in 100 µL/mouse; Dako, USA). After 15 min, dorsal skin and ears were collected. To stimulate MRGPRX2 receptor after Evans blue injection, 10 µL of a solution containing 1 µM of meglumine diatrizoate (Sigma–Aldrich), gadobutrol (Sigma–Aldrich), and (R)‐ZINC‐3573 (Sigma–Aldrich) were administered by intraplantar injection in one paw and the vehicle was administered in the other paw. Evans blue extravasation was visualized 15–20 min later and paws were collected. Samples were dried for 24 h at 55–60°C, weighed, Evans blue was extracted by a 24‐h incubation in formamide at 55–60°C and quantified by the absorbance at OD_620nm (Tecan, USA).

Compound 48/80 (Sigma–Aldrich), levofloxacin (Sigma–Aldrich), meglumine diatrizoate (Sigma–Aldrich), gadobutrol (Sigma–Aldrich), (R)‐ZINC‐3573 (Sigma–Aldrich), human IgE (CalbioChem, USA), and rabbit polyclonal anti‐human IgE (Dako, USA) were obtained from respective companies.