Most LVs located in the proximal mesenteric lymphatic vessels of S1pr1 ^iΔLEC mice were normal. (A) Mesenteric lymphatic vessels from the sections corresponding to the duodenum, jejunum, and ileum were dissected from 3-mo-old S1pr1^iΔLEC (TM@P1–7) mice, cleaned, and cannulated (top row). Subsequently, LV function test was performed. While gradually increasing the Pout, the pressure (Psn) and vessel diameter were measured behind the LVs. Duodenal and jejunal LVs did not have any pressure back leak (second row). Consequently, those vessels did not expand in diameter as Pout was raised (bottom row). In contrast, an LV from the ileum exhibited back leak, as indicated by increasing Psn and diameter with increasing Pout. (B) Quantification of back leak of LVs harvested from the duodenum and jejunum versus ileum of control and S1pr1^iΔLEC mice. Statistics: (B) n = 31 control (duodenum and jejunum), n = 28 control (ileum), n = 15 S1pr1^iΔLEC (duodenum and jejunum), and n = 26 S1pr1^iΔLEC (ileum) LVs. LVs from 3-mo-old S1pr1^iΔLEC (TM@P1–P7) and 10-mo-old S1pr1^iΔLEC (TM@8w) were combined as S1pr1^iΔLEC for this analysis. *P < 0.05; **P < 0.01.