Fig. 4: Blooding sucking experiment.

a Five groups of lampreys were used for blood-sucking experiment. Group 1 is the buccal gland collected from lampreys before blood-sucking; Group 2 is the feeding-site from the host fish (catfish); Groups 3 and 4 are non-feeding sites from the host fish; and group 5 is the buccal glands collected from lampreys after blood-sucking. b Principal component analysis (PCA) score plots of the metabolic profiles of the 5 sample groups (n = 3 for each group). Measurement of relative peak areas of N-formylkynurenine (c), L-Kynurenine (d), kynurenic acid (e), 3-hydroxykynurenine (f), prostaglandin E₃ (g), prostaglandin F₂ alpha (h), prostaglandin E₂ (i) and prostaglandin J₂ (j). The data are shown as the mean ± SD (n = 3). The metabolite abundances between different groups were compared using one-way analysis of variance (ANOVA); If deemed significant (p-value < 0.05), post hoc multiple comparison analysis was performed with false discovery rate correction; ns, not significant; *p < 0.05; **p < 0.01.