Hypertensive effect of calcilytic NPS 2143 administration in rats

Secretion of parathormone (PTH), the main parathyroid hormone, which is under the control of the calcium sensing receptor, might be inhibited by calcimimetics and stimulated by calcilytics. Parathyroid glands also secrete parathyroid hypertensive factor. Recently, it was shown that calcimimetic NPS R-568 induced decreased blood pressure in spontaneously hypertensive rats (SHR) in the presence of parathyroid glands. Therefore, the aim of this study was to determine whether administration of the calcilytic NPS 2143 provoked an increase of mean arterial blood pressure (MAP) in normotensive rats. We used male Wistar rats anaesthetized with thiopental. Clearance experiments were performed and the effect of bolus, 1 mg/kg body weight i.v. of NPS 2143 on MAP in the presence and absence of thyroparathyroidectomy (TPTX) was monitored continuously. Calcilytic properties of NPS 2143 were confirmed directly by a significant (P < 0.05) increase of plasma PTH concentration, and indirectly by a rise of plasma Ca(2+) concentration and urinary fractional phosphate excretion (FE Pi). NPS 2143 administration markedly (P < 0.05) increased MAP, calculated as the difference ( Delta ) in MAP between sequential measurements and the time of bolus injection of calcilytic. The observed increase of blood pressure in the NPS 2143 group was also significant (P < 0.05) compared with the control group. Performance of TPTX prevented the hypertensive effect of NPS 2143. We conclude that NPS 2143 is responsible for increased blood pressure in rats in the presence of parathyroid glands.