Study of growth kinetics and morphology in limbs transplanted between animals of different ages

The influence of age and maturity on longitudinal skeletal growth was studied using heterotopic limb transplantation with microvascular anastomoses between syngeneic male Lewis rats of different ages. Longitudinal growth of the tibia and growth plate morphology were compared after transplantation between isochronografts (juvenile-to-juvenile and adult-to-adult), heterochronografts (juvenile-to-adult), and unoperated limbs. Four animals comprised each experimental group, except for the juvenile-to-adult heterochronograft group, which had six animals. Limbs were measured at 2-week intervals until sacrifice at 7 weeks. All transplanted limbs demonstrated significant longitudinal growth with maintenance of growth plate morphology and columnar organization. Despite being subjected to an adult hormonal environment, the juvenile tibias transplanted into adult hosts grew 12.0 +/- 1 mm--not significantly different from the unoperated juvenile controls, which grew 12.2 +/- 1 mm. Adult isochronografts showed continued growth of 3.1 mm, which was not significantly different from the unoperated control. Juvenile isochronografts demonstrated decreased growth when compared to unoperated limbs. Maintenance of growth in juvenile limbs transplanted to adults suggests a permissive effect of the hormonal milieu and that ultimate skeletal length is primarily determined by factors inherent in each physis. The use of vascularized transplantation of limbs in syngeneic animals of different ages offers a unique method of altering the hormonal and maturational milieu of the growth plate.