Catch-up growth is associated with delayed senescence of the growth plate in rabbits

In mammals, release from growth-inhibiting conditions results in catch-up g rowth. To explain this phenomenon, we proposed the following model: 1) The normal senescent decline in growth plate function depends not on age per se , but on the cumulative number of replications that growth plate chondrocyt es have undergone. 2) Conditions that suppress growth plate chondrocyte pro liferation therefore slow senescence. 3) After transient growth inhibition, growth plates are thus less senescent and hence show a greater growth rate than expected for acre, resulting in catch-up growth. To test this model, we administered dexamethasone to growing rabbits to suppress linear growth. After stopping dexamethasone, catch-Lip growth occurred. In distal femoral growth plates of untreated controls, we observed a senescent decline in th e growth rate and in the heights of the proliferative zone, hypertrophic zo ne, and total growth plate. During the period of catch-up growth, in the an imals previously treated with dexamethasone, the senescent decline in all t hese variables was delayed. Prior treatment with dexamethasone also delayed epiphyseal fusion, These findings support our model that linear catch-up g rowth is caused, at least in part, by a delay in growth plate senescence.