TISSUE DIFFERENTIATION AND CORRELATED CHANGES IN ENZYMATIC-ACTIVITIESDURING PRIMARY ANTLER DEVELOPMENT IN FALLOW DEER (DAMA-DAMA)

Background: Deer antlers are useful models for studying bone growth an d biomineralization in mammals. To achieve a better understanding of t he mechanisms underlying the formation of primary cranial appendages i n deer, the present study relates the histogenesis of primary antlers to changes in enzymatic (phosphatase) activities in the different tiss ue zones of this organ. Methods: The growing tips of the primary antle rs (4.3 to 5 cm in length) were removed from five fallow bucks, aged a bout 10 months. Part of the material was processed for light microscop y. The other part was cryofixed, and the different histologically defi ned regions were analyzed for the activities of alkaline phosphatase ( ALP) and tartrate-resistant acid phosphatase (TRAP) as well as for the concentrations of inorganic and organic phosphate. Results and Conclu sions: Histologically, the primary antler could in distoproximal direc tion be divided into eight different zones (dermis; perichondrium; zon es of cartilage formation, hypertrophy, mineralization, and degenerati on; primary spongiosa; secondary spongiosa). The histological results demonstrate that the elongation of the primary antler proceeded throug h a modified form of endochondral ossification, resembling that seen d uring formation of pedicles and secondary antlers. The concentrations of the extractable activities of ALP and TRAP progressively increased from the perichondrium to the zone of cartilage mineralization. Thus, highest activity of TRAP during primary antler formation occurred at a n earlier stage of tissue differentiation than in somatic endochondral ossification, where the enzyme is a biochemical marker of osteoclasti c activity during bone remodeling. The present results might reflect t he presence of osteoclastic precursor cells in the zone of cartilage m ineralization as an adaptation to the rapidity of antler growth. Our f indings of the contents of extractable ALP, inorganic and organic phos phate in the different tissue zones of the developing primary antler a re in good agreement with previous studies analyzing epiphyseal growth plates and point to the fact that ALP causes a rise in inorganic phos phate and the removal of inhibitors for mineralization, like pyrophosp hate. (C) 1995 Wiley-Liss, Inc.