Involvement of polyamines in the proliferation of bovine parathyroid cells

An active form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], is involved in the regulation of parathyroid cell proliferation as well as of parathyroid hormone synthesis. We examined the effects of 1,25-(OH)2D3 on the proliferation of parathyroid cells in relation to their effects on ornithine decarboxylase (ODC) activity. Exposure of bovine parathyroid cells to serum caused an elevation in [3H]thymidine incorporation, which was preceded by a rise in ODC activity. The biodegradative enzyme, spermidine/spermine N1-acetyltransferase (SAT) activity did not change by 12 h after serum exposure. Preincubation of the cells with 10(-8)M 1,25-(OH)2D3 for 48 h attenuated the serum-induced rise in ODC activity by 12 h. alpha-Difluoromethylornithine (DFMO), a specific inhibitor of ODC, inhibited the serum-stimulated [3H]thymidine incorporation. Simultaneous addition of 25 microM putrescine reversed the inhibitory effect of DFMO. In summary, it was strongly suggested that polyamine is intimately involved in the proliferation of parathyroid cells and that 1,25-(OH)2D3 inhibited parathyroid cell growth through suppression of ODC activity.