Effects of age and dietary restriction on the kidney glomeruli of mice: observations by scanning electron microscopy

A study was undertaken to examine, by scanning electron microscopy (SEM), the kidney glomeruli of control mice 1 mo, 10 mo, and 24 mo of age, as well as dietarily restricted mice 10 mo and 24 mo of age. One month old female C57BL/6J mice were offered one of the following: 1) a control diet containing 24% protein fed ad lib; 2) the control diet fed on alternate days (intermittently fed); or 3) a diet containing 4% protein fed ad lib. Animals were sacrificed, by aldehyde perfusion at 1 mo, 10 mo, and 24 mo of age. The kidneys were sliced and prepared for SEM. There was a significant age-related increase in glomerular diameter and amount of microvilli on the podocyte surface (microvillus index). Although the diameters of the podocytes increased approximately 20% with age, these differences were not statistically significant. Feeding a 4% protein diet resulted in smaller diameters of glomeruli and podocytes as well as smaller microvilli indices as compared to those of control animals. Although similar differences were observed in the kidneys of intermittently fed animals, only the microvillus index was statistically significant. Therefore, dietary manipulations, which have been shown to increase life span, result in marked morphological differences when compared to control animals.