A Stereological Study of Key Histological Structures in the Kidneys of Rats from Young to Old Age

Abstract

Quantitative (morphometric) study of the total amounts (per organ) and mean sizes of histological structures in individuals from young to old are essential for the understanding of age-related organ changes; stereological techniques are essential, reliable tools to obtain the quantitative data. Stereological study of all renal components, especially renal tubules, was lacking in age-related kidney studies and few studies used rats older than 24 months of age for a stereological analysis of the aging kidney. In the present study isotropic uniform random renal sections (methacrylate-embedded) were obtained from male Sprague-Dawley rats (8−9 per age-group) randomly sampled from a single cohort of normal animals at the ages of 3, 6, 12, 24 and 36 months, respectively. The sections were measured using various stereological methods to estimate the total amounts (per kidney) or mean sizes of key renal structures. The results demonstrated that the volume of kidney and the total volume or length of renal tubules increased continually from 3 to 24 months of age and then plateaued between 24 and 36 months of age. The total volume of renal corpuscles, glomeruli, Bowman's space or interstitial tissue and the mean volume of renal corpuscles or glomeruli increased continually from 3 to 24 months and further until 36 months of age. The total number of glomeruli remained essentially constant and the relative volume of the cortex or medulla and the relative length of different segments of the renal tubules remained basically stable throughout the ages. Less than 5% of the renal corpuscular or tubular profiles were apparently atrophied at 24 or 36 months of age. The age-related results suggested that the rat renal tissues continued to develop adaptively or work actively, from young to old, to maintain normal physiological functions and the aging change in the kidney was primarily a compensatory or hypertrophic histological change.