RESUMEN
Disturbed calcification of the growth plate and stunting is a frequent finding in vitamin D-deficiency rickets, vitamin D-dependency rickets and renal osteodystrophy, illustrating that chondrocytes are a target for vitamin D. This observation prompted an investigation of Ic, 25-dihydroxy vitamin D3 [1,25(OH)2D3] receptor expression and action of vitamin D metabolites on chondrocyte proliferation. In tibial growth plates and in primary cultures of tibial growth cartilage of male Sprague-Dawley rats (80 g) specific binding of [3H]-1,25(OH)2D3 was noted. Scatchard analysis revealed the presence of a single class of non-interacting binding sites. Kd was 10(-11) M irrespective of growth phase. The binding macromolecule had a sedimentation coefficient of 3.5 S. Interaction with DNA was demonstrated by DNA-cellulose affinity chromatography. By immunohistology, growth cartilage cells (rabbit tibia) were shown to express nuclear 1,25(OH)2D3 receptors, most prominently in the proliferative and early hypertrophic zone. This corresponds to binding data which showed highest binding of 1,25(OH)2D3 in the logarithmic growth phase (12,780 molecules/cell versus 4,538 molecules/cell in confluent cells) in primary cultures of growth plate chondrocytes. In the presence of delipidated fetal calf serum 1,25(OH)2D3 had a biphasic effect on cell proliferation and density, i.e. stimulation at 10(-12) M and dose-dependent inhibition at 10(-10) M and below. Inhibition was specific and not seen with 24 (R), 25-dihydroxy-vitamin D3 or dexamethasone. Growth phase-dependent 1,25(OH)2D3 receptor expression and specific effects of 1,25(OH)2D3 on chondrocyte proliferation in vitro point to a role for vitamin D in the homeostasis of growth cartilage of the rat.