Morphometric studies of catch-up growth in the rat.

It would appear from these results that no simple relationship exists between the ability of the animal to achieve complete catch-up and the degree to which it has fallen behind controls, the maturity of the region at the time the insult is applied, or the relationship of the insult to the timing of the peak growth velocity. The findings of Widdowson and McCance [1963], that postweaning undernutrition has far less serious consequences than preweaning undernutrition, are, however, confirmed. The age of the animal at the time that the insult is applied and the degree to which it falls behind controls would both seem to make a contribution to the eventual catch-up, older animals being better able than younger ones to recover fully from the same degree of deficit. The results show that different regions of the skeleton respond differently to periods of undernutrition, both in the degree to which they fall behind control values and in their ability to achieve complete catch-up. The potential for catch-up is known to vary, depending on the state of cell multiplication at the time that the insult is applied [Enesco and LeBlond, 1962; Winick and Noble, 1965, 1966] and periods of undernutrition are known to result in a disturbance in the structure of cartilage [Silberberg, 1968; Dearden and Espinosa, 1974; Dearden and Mosier, 1974]. Presumably the results presented here reflect differences in the various cartilages of the regions being examined, complete catch-up being impossible in some regions due to permanent abnormalities of structure and/or function having been induced.