Induction by Parathyroid Hormone of Ornithine Decarboxylase in Rabbit Costal Chondrocytes in Culture1

The activity of ornithine decarboxylase (ODQ in rabbit costal chondrocytes in culture markedly increased after addition of parathyroid hormone (PTH), reaching a maximum 4 to 5 h after PTH addition. The effect of PTH was dose-dependent both in the presence and absence of fetal calf serum. Addition of cycloheximide or actinomycin D prevented the induction of ODC by PTH. Calcitonin, 1,25-dihydroxyvitamin D3, and vitamin A had no stimulatory effect on the activity of ODC, and did not inhibit the induction of ODC by PTH, when added with PTH. The polyamines putrescine, spermidine, and sper- propiolate, a potent inducer of hyperplastic change mine, have been linked to many processes for of epidermis (4). Recent studies by Conroy et al. growth, division, and differentiation of various and by Rath and Reddi indicated the occurrence types of cells (7, 2). Previously, we showed that of ODC and polyamines in cartilage (5, <$). Ac-ornithine decarboxylase [EC 4.1.1.17; ODC], the cumulation of polyamines is frequently found in enzyme responsible for putrescine formation and tissues showing rapid growth, but the physiological probably the rate-limiting enzyme in polyamine functions of polyamines are unknown, biosynthesis, was rapidly induced during growth We have already shown that growth-cartilag