Development and functional capacity of transplanted rat metanephroi

BACKGROUND: Transplantation of embryonic kidneys (metanephroi) offers a potential solution to the problem of kidney donor shortage. The aim of this study was to characterise the haemodynamic capacity of transplanted rat metanephroi and to determine the number and maturity of the tubules. METHODS: Metanephroi from E15 Lewis rat embryos were transplanted adjacent to the abdominal aorta of uninephrectomised adult female syngeneic Lewis rats. Twenty-one days later, a single metanephros ureter was anastomosed to the host's urinary system. Three months later animals were prepared for standard clearance measurements. RESULTS: Effective renal blood flow (149 +/- 33 microl min(-1) per g kidney weight) and glomerular filtration rate (17 +/- 9 microl min(-1) per g kidney weight), standardised to kidney weight, were significantly lower in transplanted metanephroi compared with control adult kidneys (P < 0.001); renal vascular resistance (934 +/- 209 mmHg ml min(-1) per g kidney weight) was significantly higher (P < 0.001). Nephron number in transplanted metanephroi was significantly greater than that of E21 kidneys (P < 0.01) but lower than that of postnatal day (PND) 1 kidneys (P < 0.001). Angiotensin II type 2 receptor mRNA expression, a marker of nephrogenesis, was markedly reduced in metanephroi. Aquaporins 1 and 2, epithelial Na channel and Na-K-2Cl cotransporter type 2 mRNA and protein were expressed in transplanted metanephroi; the urea transporters-A1, 2 and 3 were absent. Vascular markers (alpha-smooth muscle actin and CD31) were identified in metanephroi but their expression did not differ from that of E21 and PND 1 kidneys. CONCLUSIONS: This study shows that metanephroi continue to develop post-transplantation but only reach a stage of development equivalent to that of a normal rat kidney at birth.