Effect of short-term fasting on bone elongation rates: an analysis of catch-up growth in young male rats.

Bone elongation in the postnatal animal is a result of cellular activity during endochondral ossification. Growth plate chondrocytes undergo a differentiation cascade involving stem cell clonal expansion and cellular enlargement during hypertrophy. Nutritional status has a significant effect on rates of bone growth, and a period of accelerated growth will occur if nutritional stunting of growth in early childhood can be corrected. This study focuses on changes in rates of increase in bone length in a model of catch-up growth in 4-wk-old male rats. Animals fasted for 3 d reached a weight approximately 60% of the control littermates. By 28 d postfasting, fasted animals had regained weight to 95% of control levels. A 3-d fast caused an immediate and profound decrease in rate of growth in the proximal tibial growth plate to only 30% of that of control animals, while stopping growth in the distal tibial growth plate. During the rapid initial rate acceleration of bone elongation, growth rate in both growth plates reached that of the control littermates by 7 d postfasting. The proximal tibial growth plate then maintained rates that were 10-15% higher than control over the rest of the experimental period. By 10 d postfasting, the previously fasted animals were on the same weight/rate trajectory as the control littermates. Changes in elongation rates were reflected by dramatic changes in growth plate morphology in all cellular zones. This is the first study to directly correlate weight recovery during catch-up with growth rate responses at the level of the growth plate.