Relationships of cervical, thoracic, and lumbar bone mineral density by quantitative CT.

PURPOSE: The purpose of this work was to compare, using quantitative CT (QCT), vertebral bone mineral density (BMD) in the cervical, thoracic, and lumbar spine in healthy volunteers. METHOD: QCT of the vertebral bodies of C2, C5, T12, and L4 was performed on 50 healthy volunteers (25 women, 25 men; mean age 31.7 years). Trabecular BMD analysis was performed at each level. RESULTS: Mean BMDs (mg/cm3 calcium hydroxyapatite) for women and men were highest at C5 (BMD women/men 341.6/300.6 mg/cm3) and C2 (297.2/269.6 mg/cm3) and lowest at T12 (193.1/184.9 mg/cm3) and L4 (186.2/180.1 mg/cm3). The BMD of C2 was statistically significantly different from that of C5, T12, and L4 (p < 0.0001) for both genders. Also, the BMD of C5 differed significantly from that of T12 and L4 (p < 0.0001). The BMD of C5 showed significant gender differences (p = 0.002). Correlation coefficient showed a strong correlation between the BMD of T12 and L4 for both genders (women, r = 0.67; men, r = 0.90). CONCLUSION: Trabecular BMD of C2 and C5 measured by QCT is significantly higher than trabecular BMD of T12 and L4 in nonosteoporotic volunteers of both genders.

A functional tethered ligand thrombin receptor is present on human hematopoietic progenitor cells.

The processing of inflammatory signals occurs through a variety of mechanisms; the recent descriptions of the tethered ligand receptor for thrombin (JA Hoxie et al., J Biol Chem 268:13756, and TK Vu et al., Cell 64:1057) provide a novel route and mechanism for cellular activation after inflammation and thrombosis. Using standard flow-cytometric techniques, it has been shown that the tethered ligand receptor is found on a number of terminally differentiated hematopoietic cells including platelets, lymphocytes, and monocytes. In this paper, we show that the CD34+ subset of hematopoietic stem cells bears the tethered ligand receptor on its surface; in addition, stimulation of this receptor with the agonist peptide SFLLRN results in a dose-dependent increase in intracellular calcium levels. We also show that culturing bone marrow mononuclear cells in the presence of thrombin or the tethered ligand receptor agonist peptide results in a statistically significant increase in colony-forming units-erythroid and -granulocyte/macrophage (CFU-E and CFU-GM). Although more work is needed to establish the exact mechanism of this effect, our results suggest that activation of the tethered ligand thrombin receptor may modulate the proliferative responses of CD34+ hematopoietic progenitor cells.