A model of sterile vesicoureteric reflux in the sheep

Eighteen Coopworth ewe lambs were divided into three groups based on the initial cystourethrogram and cystometry findings at 5-7 weeks of age: group 1, 6 lambs with spontaneous low-pressure bilateral vesicoureteric reflux (VUR) on bladder filling were used to study the natural history of reflux; group 2, 5 lambs with no VUR detected were used to establish an experimental model of bilateral VUR using an unroofing surgical procedure; group 3, 7 lambs with spontaneous VUR detected during micturition had the same surgical procedure to increase the degree of VUR. All three animal groups were followed for 4-10 months. Spontaneous VUR was demonstrated in 13 of 18 lambs (25/36 ureters). The presence and severity of spontaneously occurring reflux in group 1 lambs diminished with increasing age. VUR was created successfully in group 2 and increased in degree in group 3 animals. The only significant histological finding in all three animal groups with grades II and III VUR was distal renal tubular dilatation. The sheep is a useful and readily available animal for studying VUR. During 4-10 months of follow-up, sterile reflux without bladder outflow obstruction resulted in distal renal tubular dilatation, but no renal parenchymal damage.