Aging and rates of lens-cell differentiation in vivo, measured by a chemical approach.

We describe a direct and comparatively rapid chemical approach for quantitating rates of lens epithelial cell differentiation in vivo and apply it to a study of the basis of the precipitous decrease in the rate of lens growth in the rat between about 1 and 6 weeks of age. Rates of terminal differentiation of epithelial cells into fiber cells were quantitatively described by a first-order-fractional rate constant (k) for loss of 3H-DNA (labeled from injected 3H-thymidine) from the capsule (epithelium) to fiber cells. The rate constant (expressed in days) was calculated using the half-life estimated from semilogarithmic plots of the percent of total lens 3H-DNA measured in the capsule fraction versus time after injection of 3H-thymidine. The rate constant decreased from about k = 0.18 day-1 at 6 days of age to about 0.09 day-1 at 18-20 days of age and changed little thereafter. The decrease in lens growth at very early ages in the rat is at least partially due to decreases in rates of epithelial cell differentiation.