Background: The number of glomerular capillaries were unbiasedly estimated in the very heterogeneous population of glomeruli found in rats with lithium-induced nephropathy. The glomeruli are atubular, connected to atrophic tubules, or connected to normal proximal tubules. In rats with lithium nephropathy, hypertrophy is found in glomeruli with normal tubular connection. This hypertrophy may take place by an increase in the number, length, or diameter of the capillaries.
Experimental design: In serial sections, the glomeruli were sampled at random and followed to detect whether they were connected to an atrophic tubule, a normal proximal tubule, or no tubule at all. On 1-micron-thick serial sections, the number of capillaries was estimated using a method based on a topologic definition of the capillary. The number was estimated for three categories of glomeruli: normal glomeruli from control animals, hypertrophic glomeruli connected to normal proximal tubules from lithium-treated animals, and atrophic glomeruli being either atubular or connected to atrophic tubules from lithium-treated animals. On the same sections, stereologic methods were used to estimate the cross-sectional area and the length density of the glomerular capillaries.
Results: The mean number of capillaries in normal, hypertrophic, and atrophic glomeruli was 188 +/- 26 (+/- SD), 271 +/- 32 (+44%), and 65 +/- 12 (-65%), respectively. Whereas the total length of the capillaries per glomerulus was increased in hypertrophic glomeruli and decreased in atrophic glomeruli compared to normal glomeruli, the mean capillary length of 48.3 +/- 3.7 microns, and 53.0 +/- 11.3 microns in the hypertrophic and atrophic glomeruli, respectively, was significantly higher than the 41.0 +/- 4.6 microns in the controls.
Conclusions: We conclude that in lithium-induced nephropathy, glomerular hypertrophy is mainly due to the increased numbers of capillaries, whereas the increase in the individual capillary length is of lesser importance.