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Biomedical subjects

C R Howlett

Publications and source records attributed to C R Howlett.

69 records · Page 4Linked to original sources
PubMed1979

The fine structure of the proximal growth plate of the avian tibia.

The ultrastructure of the proximal tibial growth plate of the 7 weeks old chicken has been described. Little ultrastructural difference could be ascertained between growth plates examined from normal white leghorn and commercial broiler chickens. The growth plate may be divided into five zones: interstitial, proliferating, prehypertrophic, hypertrophic, and degenerating hypertrophic. These zones reflect a maturation of chondrocytes, beginning with a stage of high mitotic and cytoplasmic activity passing through a stage of active secretion of matrical components (prehypertrophic and hypertrophic) and ending with degeneration of the cells and calcification of the matrix. Mineralization of the matrix appears to be initiated within matrical dense bodies, as in the mammal. Single hydroxyapatite crystals are first encountered about 0.1 mm proximal (i.e. towards the knee) to the limit of metaphyseal blood vessel ingrowth, while dense calcification is observed 0.1 mm distal to the tips of these metaphyseal vessels. The diameter of microfibrillary collagen in the growth plate matrix ranges from approximately 9 nm in the proximal zones to 19 nm in the distal zones. Many of the fibrils in the distal zones have a more or less distinct periodicity. Other major elements of the growth plate matrix are the ruthenium red-stained syncytial aggregates of mucopolysaccharides which are probably derived from the granules within the large intracellular Golgi vesicles. These findings have led the author to conclude that, while light microscopy indicates that avian and mammalian growth plates have very different structures, electron microscopy finds many similarities, suggesting that the physiological control mechanisms in these two vertebrate classes have much in common.

Animals↗
PubMed1978

The inheritance of tibial dyschondroplasia in broilers.

A breeding programme to develop a line of chickens with a high incidence of tibial dyschondroplasia (TD) from Australian broiler stock is described. Despite the absence of a control flock, this programme has demonstrated that selection in a broiler population can rapidly increase the incidence of TD. There was consistent circumstantial evidence of the presence of a major sex-linked gene, the recessive allele of which is associated with an increased incidence of TD. The realised heritability estimates (obtained in the absence of a control flock) consistently exceeded 1.00, suggesting the presence of an environmental trend favourable to the onset of TD over the four generations of this investigation. There was a high maternal component or dominance genetic component, or both, for the inheritance of TD in the final generation, suggesting that environmental factors associated with the female parent line may influence the incidence of TD in broilers.

Animals↗
PubMed1977

Movement of 125I albumin and 125I polyvinylpyrrolidone through bone tissue fluid.

The passage of tissue fluid through cortical bone has been investigated using radioactively labelled macromolecules as markers. The results suggest that in the cortex of young rabbit femur the movement of tissue fluid is in the same net direction as blood, mainly from the endosteal to the periosteal surface. Some albumin is incorporated from extravascular tissue fluid into calcified matrix at sites of bone formation. Polyvinylpyrrolidone, average molecular weight 35,000, is able to pass through extravascular tissue fluid in bone but is not incorporated into calcified matrix. In rabbits made vitamin D deficient, much less alblmin is retained in regions of bone formation than is the case with controls. Albumin adsorbs to the surface of calcium phosphate precipitates and it is suggested that this mechanism may be mainly responsible for its incorporation into bone.

Albumins↗
PubMedDate not supplied

Effect of platelet-derived growth factor on tibial osteotomies in rabbits.

The effect of exogenous platelet-derived growth factor (PDGF) BB on bone healing was tested in a pilot study using a unilateral tibial osteotomy in rabbits. Each osteotomy was injected with collagen or collagen containing 80 micrograms of PDGF. At 28 days, both tibiae from each rabbit were harvested and subjected to three-point bending to failure. The effect upon bone healing was tested by comparing the healing rates of PDGF-treated and -nontreated osteotomies with their respective normal contralateral bones. Three animals died before 28 days. The remaining 6 experimental and 5 control animals were available for assessment. Radiographically, at 2 weeks and 4 weeks, there was a clear increase in callus density and volume around the PDGF-treated osteotomies compared with the control rabbits' osteotomies. Osteotomies treated with PDGF were not statistically different in strength from their nonoperated contralateral bones. In the control group, however, the osteotomies were statistically weaker than their nonoperated (contralateral) bones. Microscopically, it was generally observed that PDGF-treated tibiae displayed a more florid and advanced state of osteogenic differentiation, both endosteally and periosteally, than the control osteotomies. Radiographic, mechanical, and histopathological data suggest that exogenous PDGF has a stimulatory effect on fracture healing.

Animals↗
PubMedDate not supplied

Laminated tears of the human rotator cuff: a histologic and immunochemical study.

Laminated tears of the rotator cuff are often lined by a cellular layer that has an appearance suggestive of synovium. This study demonstrates, by histologic and immunohistochemical means, that the lining cells are synovial. It remains unclear whether these cells arise by synovial extension from the joint or bursa, or by metaplasia in the presence of synovial fluid, and this has implications for surgical repair of laminated cuff defects. We suggest that these defects be curetted, to remove at least some of this synovial lining, before suture repair.

Adult↗
PubMedDate not supplied

Ultrastructure of bone and cartilage formed in vivo in diffusion chambers.

Osteogenic tissue formed in vivo in diffusion chambers inoculated with a suspension of marrow cells contains both bone and cartilage. Observations by transmission electron microscopy on the transitional zone between these tissues showed a mixture of osseous and cartilaginous features in both matrix and cells. Two forms of collagen, morphologically consistent with Types I and II, are found in intimate association within the same intercellular septa. The results suggest the possibility that the different collagen types are synthesized by the same cells and that the variation in cellular morphology could be associated with the changes in the type of collagen synthesized. This unique characteristic of calcified tissues formed in diffusion chambers is probably the result of isolation from direct blood circulation, mechanical stress, and cellular mechanisms of tissue breakdown.

Animals↗