Incubation of Metanephroi with Vitamin D3 Increases Numbers of Glomeruli

Abstract

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 D3 [25(OH)D3] or 1, 25-hydroxyvitamin D3 [1,25(OH)2D3] prior to implantation. The number of glomeruli in developed metanephroi three weeks post-transplantation that had been incubated with 1.0 ug/ml vitamin D3 was increased relative to the number in metanephroi that were not incubated with vitamin D3 (control), an effect that was not recapitulated by administration of vitamin D3 directly to hosts at the time of transplantation. Incubation of metanephroi with 1.0 ug/ml vitamin D3 also enhanced inulin clearances of metanephroi measured at 12 weeks post-transplantation. The hydroxylated derivative of vitamin D3, 25(OH)D3, increased glomerulus number when applied at 0.01 ug/ml but not at higher concentrations, while the twice-hydroxylated derivative 1,25(OH)2D3, failed to increase glomerulus number at any concentration tested. We conclude that incubation with vitamin D3 prior to implantation enhances inulin clearance possibly by increasing the number of glomeruli that develop post-transplantation. Our findings suggest the vitamin D3 effect is mediated locally.