Diffusion in the various zones of the normal and the rachitic growth plate.

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Abstract
Calcification of the intercellular matrix of the growth plate may make the matrix relatively impermeable to metabolites, and may lead to the death of the hypertrophic chondrocytes in the zone of calcification of the epiphyseal plate. This hypothesis was tested by measuring the diffusion coefficients of 3H-inulin and 14C-sucrose by a desorption technique in slices of growth-plate cartilage from normal rabbits, normal rats, rachitic rats and healing rachitic rats. In the normal rabbit the diffusion coefficients for 3H-inulin and 14C-sucrose were lowest in the zone of hypertrophic cells and increased progressively through the proliferative zone, reserve zone and hyaline cartilage. In the animals with rickets the diffusion coefficient of 3H-inulin in the hypertrophic cell zone was greatly increased and it returned toward normal with healing of the disease. Results of diffusion studies were correlated with the following parameters: percent matrix based on volume, hexosamine content, hydroxyproline content, percent water, percent dry matter, percent ash based on wet weight and ash as percent of dry matter. Continuous simple linear regression analysis revealed that ash content was the parameter that correlated best with the diffusion coefficients calculated from the desorption studies. Apparently, calcification of cartilage matrix significantly inhibits diffusion of nutrients to the growth-plate chondrocytes.