PubMed · 8213939
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
L Southmayd. 1993. Dialysis considerations.. https://doi.org/10.1097/00000446-199310000-00009
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Explore the source record for details and available documents.
The synthesis of 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) from its precursor, 25-dihydroxyvitamin D(3) (25(OH)D(3)), is catalyzed by the mitochondrial cytochrome P450 enzyme 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-hydroxylase). It has been generally assumed that 1,25(OH)(2)D(3) inhibits the activity of this enzyme by regulating its expression at the genomic level. We confirmed that 1,25(OH)(2)D(3) reduced the apparent conversion of 25(OH)D(3) to 1,25(OH)(2)D(3) while stimulating the conversion of 1,25(OH)(2)D(3) and 25(OH)D(3) to 1,24,25(OH)(3)D(3) and 24,25(OH)(2)D(3), respectively. However, 1,25(OH)(2)D(3) failed to reduce the abundance of its mRNA or its encoded protein in human keratinocytes. Instead, when catabolism of 1,25(OH)(2)D(3) was blocked with a specific inhibitor of the 25-hydroxyvitamin D(3)-24-hydroxylase (24-hydroxylase) all apparent inhibition of 1alpha-hydroxylase activity by 1,25(OH)(2)D(3) was reversed. Thus, the apparent reduction in 1alpha-hydroxylase activity induced by 1,25(OH)(2)D(3) is due to increased catabolism of both substrate and product by the 24-hydroxylase. We believe this to be a unique mechanism for autoregulation of steroid hormone synthesis.
STUDY DESIGN: To determine the osteogenicity of posterior longitudinal ligament ossification, the posterior longitudinal ligament obtained during anterior cervical surgery from patients with the disorder was analyzed with in vitro cultures. OBJECTIVES: To determine the osteogenicity of the posterior longitudinal ligament. SUMMARY OF BACKGROUND DATA: The osteogenicity of posterior longitudinal ligament ossification in North America requires better documentation. METHODS: The posterior longitudinal ligament obtained during anterior cervical corpectomy with fusion from seven patients, three with ossification of the posterior longitudinal ligament documented by magnetic resonance imaging and computed tomography and four with spondylosis, was blindly submitted for in vitro culture. Explants of the posterior longitudinal ligament were placed in Dulbecco modified Eagle medium with 10% fetal calf serum, antibiotics, 4 mmol/L x L-proline, and 50 mg/L ascorbic acid. After reaching confluency, cells were trypsinized, and first-passage cells were used for all osteocalcin measurements to establish their osteoblastic phenotype. Periosteal cells, previously shown to synthesize osteocalcin, were used as a positive control. The cells were incubated with 1,25(OH)2 vitamin D3 at 10E-8 M for 72 hours in serum-free medium. The supernatants were collected and frozen, after which the quantity of osteocalcin induced by exposure to 1,25(OH)2 vitamin D3 was determined using enzyme-linked immunoassay. Control replicate cultures were measured without incubation using vitamin D3. RESULTS: Ossification of the posterior longitudinal ligament cell lines responded positively with osteocalcin synthesis in the 0.1 to 0.4 ng/M range. The cell line of the patient with spondylosis alone did not respond to vitamin D3 priming. CONCLUSIONS: Posterior longitudinal ligament cells from the three North American white patients with ossification of the posterior longitudinal ligament, when cultured in vitro, synthesized osteocalcin on vitamin D3 priming, confirming their osteoblastic phenotype, whereas posterior longitudinal ligament cells from four white patients with isolated spondylosis did not.