Quantitative studies of the renal corpuscles iii: the influence of post mortem delay before taking renal tissue samples and of the duration of tissue fixation.

Comparative quantitative studies of glomeruli in biopsies of the guenon monkey kidney were made to give a numerical measure of the effect of varying periods of fixation of the biopsy tissue in Carnoy's fluid (1-2-24 hrs.), and of the effect of progressive post mortem delay before renal tissue samples were taken (2-4-6-12 hrs.). Additional aims were to determine possible quantitative differences between subcapsular, intermediate and juxtamedullary glomeruli, and to determine whether the glomerular area should be determined with reference to the inner aspect of Bowman's capsule (total area) or to tangents laid at the top of the capillary loops (corrected total area). The quantitative methods used were total and differential counts of glomerular nuclei by light microscopy and point counting for determination of glomerular and mesangial areas. Statistical evaluation was made by a two-way analysis of variance. The differential counts of nuclei were not affected by duration of fixation, nor by post mortem delay up to 12 hrs. before tissue samples were taken. The mesangial area expressed as a percentage of total area was significantly lower two hours post mortem, while total nuclear concentration was significantly lower at time 0 and two hours post mortem than at four, six and 12 hours post mortem. Total nuclear concentration increased as duration of fixation was increased, probably a reflection of tissue shrinking. Differences in nuclear concentration were also noted at different levels of the renal cortex. These differences were only apparent when the glomerular area was determined with reference to the inner aspect of Bowman's capsule, and disappeared when the corrected total area was used. It is concluded that duration of tissue fixation and post mortem delay before tissue samples were taken both affect method sensitivity, as reflected by some, not all, of the parameters measured. The numerical differences in the parameters were not large, however, and it will be the specific study which will determine whether variable fixation times and post mortem delay in obtaining tissue samples is acceptable. As most renal biopsies contain both subcapsular and juxtamedullary glomeruli there is probably no advantage in using the corrected glomerular area instead of the total glomerular area limited by Bowman's capsule.