Histochemical evidence of a functional heterogeneity in neonatal canine epiphyseal chondrocytes

Synopsis The chondrocytes of the neonatal proximal humeral chondroepiphyses of twelve purebred English pointer pups were investigated histochemically, using frozen serial sections, for chondroitin sulphate and for the following enzyme activities: lactate dehydrogenase, NAD and NADP transhydrogenases, glutamate dehydrogenase, isocitrate dehydrogenase, malate dehydrogenase, glucose-6-phosphate dehydrogenase, ATPase, succinate dehydrogenase, and UDPgalactose 4-epimerase. By using Alcian Blue with and without a prior digestion in testicular hyaluronidase, and Alcian Blue in the presence of 0.9 M magnesium chloride, it was found that about half the chondrocytes stained as if they were producing significant amounts of chondroitin sulphate. Only one enzyme, UDPgalactose 4-epimerase (which is involved in the biosynthesis of chondroitin sulphate), was found to have a similar staining heterogeneity. Therefore, it was concluded that the chondrocytes studied possessed a functional heterogenicity with particular reference to chondroitin sulphate synthesis while appearing morphologically homogeneous.