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The effect of 40- to 60-mesh hydroxyapatite (HA) granules (Calcitek, Inc., Carlsbad, CA) on the process of primary mineralization during bone healing was examined following insertion of the HA granules into rat tibial bone after marrow ablation. Response to HA was assessed by monitoring morphometric and biochemical changes in matrix vesicles, which are extracellular organelles associated with initial calcification. Following insertion of HA, matrix vesicle-enriched membranes (MVEMs) were isolated from the tissue adjacent to the implant and from the endosteum of the contralateral limb at 3, 6, 14, and 21 days and from a nonimplanted control group (t = 0). MVEM alkaline phosphatase- and phospholipase A2-specific activities were increased on days 6 (peak) and 14; phosphatidylserine content was also elevated on days 6 and 14 (peak). Comparable changes were seen in the contralateral limb but at lesser magnitudes. Morphological changes were observed as well. The number of matrix vesicles/micron2 matrix increased on days 6 (peak) and 14. The mean diameter of the matrix vesicles was elevated on days 6 (peak), 14, and 21. Mean distance from the calcifying front increased on day 6 but was decreased on days 14 and 21. These results indicated that HA behaves like bone-bonding implants in that there is a stimulation of matrix vesicle enzymes, increased phosphatidylserine content, and increase numbers of matrix vesicles. However, the increases occur only after 6 days postimplantation, indicating a delay in response when compared to normal healing. This delay is confirmed by the morphometric measurements. HA causes a reduction in the response associated with marrow ablation. In addition, the effects of HA are comparable locally and systemically but with different intensity. These observations suggest that osteogenic cells are able to compensate for the inhibitory effects of HA and primary calcification involves normal matrix vesicle production and maturation, if somewhat delayed and reduced in magnitude. The ability to support primary mineral formation may contribute to the successful bonding of HA with surrounding osseous tissue.

Critical events in the adaptation of osseous tissues to implant materials involve initial calcification of the newly synthesized bone. Previous studies indicated that bone-bonding but not nonbonding glass ceramics increase the matrix vesicle number, thereby compensating for delayed maturation of the extracellular organelles. The present study assessed whether this was also true for metal implants commonly used in orthopaedics and oral medicine. Bone-bonding titanium (Ti) or nonbonding stainless steel (SS) implants were placed in the right tibias of Sabra rats following ablation of the marrow. At 3, 6, 14, and 21 days postinjury, newly formed endosteal bone in the treated and contralateral limbs was removed and matrix vesicle-enriched membranes isolated. Alkaline phosphatase and phospholipase A2 specific activities and phosphatidylserine (PS) content were determined and compared with those of a nonsurgical control group. Results show that matrix vesicle alkaline phosphatase and phospholipase A2 activity and PS content was increased in the Ti-implanted limbs at 6 (peak), 14, and 21 days, although at levels less than observed in normal healing. Alkaline phosphatase activity remained elevated throughout the healing period. In contrast, these parameters were markedly inhibited in the SS-implanted limbs with respect to Ti or to normal healing. Both implants altered the systemic response associated with marrow ablation, but in an implant-specific manner. The results support the hypothesis that cells adjacent to bone-bonding materials can compensate for negative effects on primary mineralization during osteogenesis, whereas cells adjacent to nonbonding materials either do not compensate or are further depressed. The data support the use of the rat marrow ablation model as a tool for rapid, initial assessment of biomaterials in bone.

SUMMARYBulls treated with ethylene dibromide (EDB), either by oral administration of ten doses of 4 mg/kg body weight on alternate days or by a single intraperitoneal injection of 110 -120 mg of this compound into the fluid surrounding each testis, exhibited sperm malformations up to total disintegration of the sperm cells. The malformations appeared in the ejaculates collected about two weeks after the first oral dose or after the injection, and persisted for about one and two months after the last oral dose or the injection, respectively. It appears that ethylene dibromide interferes with the normal processes of spermiogenesis and sperm maturation.

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