Incubation of Metanephroi with Vitamin D3 Increases Numbers of Glomeruli

To characterize actions of vitamin D3 on metanephroi transplanted from rat embryos to adult recipients, we incubated metanephroi with or without 0.01, 0.1 or 1 ug/ml vitamin D3, 25-hydroxyvitamin D(3) [25(OH)D(3)] or 1, 25-hydroxyvitamin D(3) [1,25(OH)2D(3)] prior to implantation. The number of glomeruli in developed metanephroi three weeks post-transplantation that had been incubated with 1.0 ug/ml vitamin D(3) was increased relative to the number in metanephroi that were not incubated with vitamin D(3) (control), an effect that was not recapitulated by administration of vitamin D(3) directly to hosts at the time of transplantation. Incubation of metanephroi with 1.0 ug/ml vitamin D(3) also enhanced inulin clearances of metanephroi measured at 12 weeks post-transplantation. The hydroxylated derivative of vitamin D(3), 25(OH)D(3), increased glomerulus number when applied at 0.01 ug/ml but not at higher concentrations, while the twice-hydroxylated derivative 1,25(OH)(2)D(3), failed to increase glomerulus number at any concentration tested. We conclude that incubation with vitamin D(3) prior to implantation enhances inulin clearance possibly by increasing the number of glomeruli that develop post-transplantation.Our findings suggest the vitamin D(3) effect is mediated locally.