Effect of aluminium load on parathyroid hormone synthesis

Background. Aluminium overload leads to parathyroid hormone (PTH) suppressi on. However, it is unclear whether a decrease in synthesis or release of th e hormone is mainly involved. The aim of this study was to assess the effec t of an acute administration of aluminium on PTH synthesis and release in r ats with chronic renal failure and secondary hyperparathyroidism. Methods. The study was performed using 100 adult male Wistar rats (body wei ght 443 +/- 54 g). 7/8 nephrectomy was performed and the rats were maintain ed on a high dietary phosphorous intake. Five weeks after surgery, the rats were randomly divided into two groups, one loaded with aluminium (ALCl(3)) and the other given placebo. Aluminium or placebo were administered i.p. f or two consecutive days. The placebo group received saline at the same pH a s the aluminium solution. After 2 weeks, serum calcium, phosphorous, creati nine, PTH, and aluminium were measured. The parathyroid glands were removed and PTH messenger RNA (mRNA) was measured by northern blot. Intact PTH was measured by IRMA (Rat PTH(R), Nichols Institute). Results. No differences in serum PTH levels were found between the two grou ps after 5 weeks of renal failure. At the end of the study the rats given a luminium had higher aluminium levels than the placebo group and lower PTH l evels. No significant differences were found for calcium, phosphorous, rena l function, or body weight. PTH mRNA expression was lower in the aluminium group than in the placebo group. Conclusion. The administration of aluminium in rats with chronic renal fail ure resulted in reductions in serum PTH and PTH mRNA. Thus far, previous st udies had demonstrated that aluminium suppressed PTH release. The present f indings suggest that PTH synthesis is also reduced.