The Effect of Ageing on the Total Volumes of the a and B Cells in the Islets of Langerhans of the Rat

In previous attempts to determine the total volumes of the A and the B cells in the islets of Langerhans, separately, no regard was paid to possible differences between the individual mean cell volumes of the two cell types. In the rat it is shown that considerable error results if this fact is neglected, since the mean individual volumes of the B cells were more than three times as large as those of the A cells. By combining determinations of the total islet volume with point sampling, caryometry and differential cell counts, the separate total A and B cell volumes have been estimated in 40 rats of different ages: new-born, 5, 100 and 480 days old. While the B/A cell number ratio was significantly lower at birth than at 5 days, a comparison of the total volumes of the two cell types showed that their volume proportions were the same at both periods. This was explained by the changes in the cell number ratio being compensated by changes in the individual mean cell volume, the total volume ratio thus being unaltered. The percentage volume contribution of the A cells was found to increase with age. In the new-born rats the volume was 11.28 percent compared with 13.57 percent in the oldest animals. An analysis of variance of all four age groups confirmed that real differences existed. On the other hand a statistically significant decrease, with age, in the relative volume of the B cells was noted. In new-born animals the value was 83.16 percent compared with 76.82 percent in 480 days old animals. The relative volume of the residual islet constituents (other than A and B cells) was proportionately most affected by increase in age, the percentage contribution to the total islet volume being almost doubled in 480 days old animals as compared with the two youngest age groups. If both the total A and B cell volumes were expressed in relation to body, liver and pancreatic weights, the quotients became greatly reduced with advancing age. An exception occurred in the 480 days old animals, in which the quotients were in all cases significantly higher than in the 100 days old rats. The increase in body surface area reflected the changes in the total volumes of both A and B cells in relation to ageing considerably better than did the organ and body weights. In this case too, however, the quotient for 480 days old animals was significantly higher than in the next youngest age group. Correlation calculations, made on each individual age group, showed that a strongly positive correlation existed between the total A and cell volumes, particularly in the youngest animals. On the other hand, in no age group was there a correlation between the total volumes of either of the two cell types and the pancreatic weight.