Functional urine production and glomerular maturation from embryonic metanephros transplanted at the renal hilum in rats

End-stage renal disease remains a major global health burden, and novel regenerative strategies are urgently needed. Embryonic metanephros transplantation has emerged as a promising approach, but the optimal site for engraftment and functional maturation is unclear. In this study, embryonic day 15.5 metanephroi with attached bladder (MNB) were transplanted into adult rats at three sites: the renal hilum, renal subcapsular space, and omentum. After four weeks, grafts were assessed for survival, vascularization, nephron differentiation, and functional urine production. Compared with subcapsular and omental sites, hilum transplantation yielded markedly improved graft revasculari­zation and glomerular maturation, as demonstrated by enhanced expression of podocyte and tubular markers, as well as reduced interstitial fibrosis. Importantly, transplanted kidneys at the hilum produced urine containing creatinine and urea nitrogen, confirming functional integration with the host. These findings highlight the renal hilum as a superior anatomical niche for embryonic kidney transplantation, providing enhanced vascular supply and a microenvironment conducive to functional maturation. This work provides foundational evidence for the translational potential of renal hilum implantation as a strategy to generate functional renal tissue in vivo.