SUMMARY
Recently, cell loss by necrosis has been demonstrated in the zona reticularis of the adrenal cortex; such loss is a prerequisite of the centripetal migration theory of adrenocortical cell renewal. Consequently a method has been evolved for the estimation of the rate of cell loss from the z. glomerulosa in prepubertal male rats aged 14 days.
The method depends upon measurement of the doubling time for the z. glomerulosa by weighing and serially sectioning adrenal glands at ages from 3 to 120 days, combined with point-counting. The doubling time for the z. glomerulosa at 14 days of age was 120 h.
A continuous labelling technique was used to estimate the growth fraction and the cell cycle time. In the z. glomerulosa these were 0·80 and 87 h respectively. These values gave an estimate of the cell production or birth rate of 0·00676 cells/cell/h, or 0·676 cells/100 cells/h, and consequently the potential doubling time (assuming no cell loss) was 102 h. Since the actual doubling time exceeds the potential doubling time, cells must be lost from the z. glomerulosa. This cell loss was found to be taking place at a rate of 0·0010 cells/cell/h, or 0·10 cells/100 cells/h, and the cell loss factor (ϕ) was 0·15.
Since necrosis has only been demonstrated in the z. reticularis, and evidently does not occur in the z. glomerulosa, this cell loss rate can be considered to represent the rate at which cells migrate from the z. glomerulosa. It is proposed, therefore, that in the prepubertal animal at least, centripetal cell migration does occur.
Comparison of BrdUrd and [3H]TdR incorporation to estimate cell proliferation, cell loss, and potential doubling time in tumor xenografts