Search PubMed⌕ Search

Biomedical subjects

D S Howell

Publications and source records attributed to D S Howell.

122 records · Page 7Linked to original sources
PubMed1968

Partition of calcium, phosphate, and protein in the fluid phase aspirated at calcifying sites in epiphyseal cartilage.

A reproducible method, adapted from renal micropuncture techniques, was developed for sampling 10-40 mmul of a clear fluid from epiphyseal cartilage of normal or rachitic rats in vivo, either from the hypertrophic cell zone (C(f1)) or surface resting cell cartilage (L(f1)). Characterization of this fluid depended upon quantitation of protein, total inorganic phosphate (P(it)), total calcium (Ca(t)), nucleotide, and hemoglobin in volumes of 20 mmul. Established methods for macroscale measurements of each of these parameters have been modified to permit direct spectrophotometric readings on samples of 10(-10)-10(-11) g. The fluid from hypertrophic and peripheral resting cell cartilage was of an extracellular nature as evidenced by a high chloride and sodium, as well as low potassium, protein, and nucleotide content. The pH of fluid isolated from endochrondral plates in vivo was measured under oil as a function of P(CO2) and the computed bicarbonate was elevated above concurrent serum levels. After ultracentrifugation of C(f1) of normal, rachitic, and healing rachitic animals, nonprotein-bound calcium (Ca(f)) and phosphate (P(if)) were determined on supernatant fluids. The hypertrophic cell cartilage fluid of rachitic rats was distinguished by a high ratio C(f1)/serum of P(if). This ratio returned to normal during treatment of rickets. The upper limit for ionic activity A(1) Ca(++) x A HPO(4) (=) was too low to initiate precipitation of brushite or dicalcium phosphate but was in a range of supersaturation in respect to crystalline apatites. Thus these data are consistent with initiation of calcification by heterogeneous nucleation of mineral in the septal matrix but can be reconciled alternately with a precipitation mechanism only if the site of initial mineral phase separation is outside the septal matrix.

Animals↗
PubMedDate not supplied

Pyrophosphate release by osteoarthritis cartilage incubates.

Incubates of articular cartilage from young but not mature rabbits, as well as growth plate cartilage, elaborated PPi into basel Eagle's medium during a 4-hour period. Control rabbit synovial membrane and ear cartilage elaborated negligible amounts of PPi. The PPi was shown to be nondialyzable but could be dissociated from the alkaline phosphatase by ultracentrifugation. In 16 patients with osteoarthritis a substantial output of PPi by samples of articular cartilage from the knee was demonstrated. The present authors believe that either rapid cell division and matrix synthesis found in the base of ulcerating osteoarthritic cartilage or remodeling calcified sites comprise the origin of the PPi in such osteoarthritic cartilage. They further theorize that this PPi output accounts for a considerable fraction, if not all, of the elevated PPi levels found in synovial fluid of patients with osteoarthritis.

Aged↗
PubMedDate not supplied

Calcificaiton of growth plate cartilage with special reference to studies on micropuncture fluids.

No final comprehensive hypothesis of the chain of events involved in inhibition of calcification can be constructed at the present time. The flow diagram in Figure 1 is presented only as a working hypothesis currently used by the authors. Insofar as the Cfl is representative of native factors at calcifying sites, none of the major theories on the nature of mineral formation at present seem excluded. As in the fields of clotting and complement pathways, where backup systems seem to operate, one should not be surprised if more than one system operates in cartilaginous calcification.

Animals↗