PARATHYROID AND SERUM-CALCIUM RESPONSE IN ACUTE ALUMINUM EXPOSURE IN RENAL-FAILURE

Although PTH levels are generally raised in patients with chronic rena l failure (CRF) a fair number of patients have inadequately low parath yroid hormone (PTH) levels and low bone turnover likely due to aluminu m (Al) toxicity. This study was designed to evaluate the acute changes in PTH and ionized Ca to intravenous infusions of different doses of Al in rats with CRF. The study was divided into two phases. In phase 1 we investigated the effect of a high dose of Al (0.5 mg of AlCl3 in 0 .1 ml of saline) in rats with CRF (n = 9 rats) and in phase 2, the eff ect of a low dose of Al in CRF (n = 12 rats) was examined. The rats we re rendered uremic by the remmant kidney model. In all the studies the effect of Al was compared with a control group receiving saline infus ions (0.1 ml saline). The infusions were performed over 2 minutes into the left jugular vein and blood was withdrawn from the right jugular at 0, 45, 120 and 240 minutes in order to measure Al, Ca++ and PTH. In phase 1 after die Al infusion, serum Al remained very high, ranging f rom 879 to 1866 mug/l (p < 0.01), and the Ca++ showed a decrease both in the Al intoxicated animals and the controls (p < 0.05). This change in serum Ca++ was followed by different responses in serum PTH. As ex pected, in the controls, (saline infusion) there was a significant inc rease in PTH (p < 0.05) but in the Al intoxicated rats we observed a r eduction in PTH levels, this being highly significant between the grou ps at 240 minutes (p < 0.001). In phase 2 die serum Al levels ranged f rom 159 to 339 mug/l and there were no significant changes either in i onized Ca or PTH levels. There were also no ultrastuctural changes in the parathyroid glands. These results demonstrate that ''in vivo'' Al has a direct dose dependent inhibitory effect on PTH secretion.