Assessment of AHR to 5-HT in WT and Htr4−/− mice. Whole lung resistance (R), Newtonian resistance (Rn), tissue resistance (G), compliance (C), elastance (E), and tissue elastance (H) were measured with flexiVent. Resistance (R), Newtonian resistance (Rn), tissue resistance (G), and elastance (E) are higher and compliance (C) is lower in Htr4−/− mice relative to WT. Mean values per dose with sem are plotted (n ≥ 4/genotype). *P < 0.05 vs. WT.