Toward nephrogenesis in the pig kidney: the composite tubulo-glomerular nodule.

Background: Significant differences regarding nephrogenesis and its completion among different animal species have been reported. Since many informations on clinical conditions (i.e. asphyxia, drugs) are extrapolated from piglets, this study aimed at analyzing nephrogenesis in piglets, in order to compare it with existing data on nephrogenesis in humans.

Methods: Six male newborn piglets were subjected to euthanasia and their kidneys were harvested. Necropsy revealed no injury and no underlying pathology in any of the animals used in the experiment.

Results: The analysis of the renal cortex evidenced in all the animals studied the presence of active nephrogenesis. The sequence of events identified during porcine nephrogenesis was characterized by the appearance, in the metanephric mesenchyme, of nodules undergoing mesenchymal-epithelial transition originating a specific picture that we named the tubulo-glomerular nodule. This peculiar developmental structure gives rise to the precursor of tubular and glomerular structures, till the extrusion of developing glomeruli that progressively migrate toward the mid and deep cortex.

Conclusions: Nephrogenesis in pig is characterized by a peculiar morphological event, with marked differences compared with humans. These informations should be taken into account when the experimental data in piglets are extrapolated to humans, especially for clinical purposes.