Compensatory renal growth: modulation by calcium PTH and 1,25-(OH)2D3

To further elucidate the mechanisms by which compensatory renal growth (CRG) can be influenced by calcium and calcium regulating hormones, the influence of dietary calcium and phosphorus, parathyroid hormone (PTH) or 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was evaluated in unilaterally nephrectomized (UNI-NX) rats. These animals were sacrificed three days after UNI-NX and CRG of the remaining kidney was assessed by kidney wt, RNA and DNA gains, and by 3H-thymidine incorporation. The degree of CRG was enhanced in animals given a low dietary calcium and, conversely, was decreased in those receiving a phosphorus-poor diet. In thyroparathyroidectomized (TPTX) rats, PTH administration resulted in a dose proportional stimulation of CRG. When 1,25-(OH)2D3 was given to vitamin D deficient animals, the degree of CRG was enhanced in a dose proportional manner. In another experiment, TPTX-vitamin D deficient rats were given the same amount of 1,25-(OH)2D3 by miniosmotic pump infusion. In these animals, dietary calcium restriction, instead of stimulating, inhibited CRG. From these observations we conclude that calcium and calcium regulating hormones modulate CRG, and hypothesize that the effects observed are mediated through changes in cell calcium.