Failure of Compensatory (Catch-up) Growth in the Rat

Abstract

Extract: Growth retardation was produced in rats of the Long-Evans strain, 37–41 days of age, by withholding food, by daily injection of 5 mg cortisone subcutaneously, or by feeding a diet containing 0.1 % propylthiouracil (PTU). The duration of fasts were 24, 48, and 72 hr in different experiments. Duration of cortisone or PTU treatment was adjusted to produce maximum differences in body weight between control and experimental groups that were equivalent to the difference produced in the corresponding fast periods. Serial measurements of body weight and tail length were carried out for 60–80 days from the start of the experimental treatments. In the fasting experiments, after feeding was resumed the body weight showed a prompt acceleration and nearly complete catch-up during the course of the observations. Tail length growth decelerated during fasting and then accelerated on refeeding. This resulted in complete catch-up. After cortisone treatment there was no catch-up in body weight or tail length growth. After PTU there was a slight tendency to catch-up in body weight and tail length. The latter appeared to show a pattern of late catch-up. Growth velocity curves for these experiments showed transient changes in growth rates which eventually stabilized by 75 days of age, at about the time the animals became sexually mature. The results suggest that in the rat cortisone treatment in the postweaning period permanently damages growth mechanisms and prevents growth recovery in certain circumstances. Hypothyroidism also results in impairment in catch-up growth, but there appears to be some tendency for a delayed catch-up, especially in skeletal growth. Speculation: Failure of full catch-up by one part of an organism after transient growth arrest may be the result of either (1) damage to growth mechanisms of the part or (2) restriction of growth of the part by a control operating to maintain normal proportions in the organism.