Effects of high phosphate and low calcium on the hyperplasia of normal rat parathyroid in vitro

Objective To explore the effects of high phosphate and low calcium on the secretion function and cell proliferation in normal rat parathyroid tissues. Methods The rat parathyroid tissues resected by surgical operation under dissection microscope were incubated in vitro for 5 days and were treated with high phosphate or low calcium medium on the second day and the third day after incubation. The cell apoptosis at different time points was measured by flow cytometry. The levels of intact parathyroid hormone (iPTH) in the supernatant at different time points were detected by ELISA. The mRNA levels of prepro-PTH and proliferating cell nuclear antigen (PCNA) were measured by real-time PCR, while the protein levels of PCNA after the 24-hour treatment with high phosphate or low calcium medium were measured by Western blotting. Results Flow cytometric analysis showed that the percentage of normal living cells on the first day and the second day after incubation was significantly higher than that on the third day to the fifth day after incubation in the rat parathyroid tissues (all P 85%) under normal or high phosphate medium. There was no significant difference in the daily iPTH level on the first day to the fifth day after incubation under normal medium. Compared with normal medium, the iPTH level in the supernatant under high phosphate medium increased (P<0.05), and the expressions of preproPTH mRNA and PCNA in parathyroid tissues were significantly up-regulated (both P<0.05) after the 24-hour treatment with high phosphate medium. Compared with normal medium, the iPTH level in the supernatant under low calcium medium increased (P<0.05), and the expression of preproPTH mRNA in parathyroid tissues was significantly up-regulated after the 24-hour treatment with low calcium medium (P<0.05). Conclusions It is feasible to incubate the parathyroid issues from rats in vitro, and the best incubation time should be within 2 days. Low calcium and high phosphate stimulation could increase the synthesis and secretion of PTH, while high phosphate can also promote the cell proliferation, which is an important factor for the regulation of parathyroid function in physiological state. Key words: Hypocalcemia; Parathyroid; Hyperplasia; Proliferating cell nuclear antigen; Hyperphosphatemia