Unbiased estimation of total beta-cell number and mean beta-cell volume inrodent pancreas

We describe a method for unbiased assumption-free estimation of the total n umber of beta-cells and the mean p-cen volume in mouse and rat pancreas bas ed on light microscopy. Such a method, which takes advantage of one of the most recent developments in stereology, the fractionator, has not previousl y been described. It relies on repeated fractionation of the tissue using s ystematic uniform random sampling combined with an unbiased counting princi ple. The method was applied to eight BALB/cBom male mice (56 days) and six Lewis/MOL male rats (47 days). In mice, the total number of beta-cells was 1.06+/-0.07x10(6) (mean+/-SEM) per pancreas with a mean beta-cell volume of 1280+/-17 mu m(3), while in rats the total beta-cell number was 2.76+/-0.4 2x10(6) per pancreas with a mean beta-cell volume of 1170+/-65 mu m(3). Fur thermore, the results showed that in both species the biological variabilit y in the total beta-cell volume is due to differences in the number of beta -cells rather than variability of the mean beta-cell volume. The method can be used to give a precise description of number and volume of beta-cells a t different ages, and will make it possible to estimate the contributions o f hyper/hypotrophia and hyper/hypoplasia to a given induced or spontaneous change in the total beta-cell mass.