Bone aging.

Bone matrix of 28-month-old (senescent) rats, compared with 13-month-old rats, is strikingly deficient in the capacity to induce bone formation. Similarly, implants of senescent matrix into one-month-old, rapidly-growing rats (weanlings) produce more bone than in 13-month-old adult recipients, but not nearly enough to compensate for deficiency in the matrix of senile bone. Matrix prepared from the bone of 13-month-old rats also produces almost no cartilage and significantly lower yields of new bone in 28-month-old (senescent) than 13-month-old rats. These observations suggest that progressive decline in the matrix morphogenetic activity of bone occurs with time in adult life. This decline is a tissue specific index of bone aging, and may contribute to the reduction of bone mass that normally occurs with senescence.