Transperitoneal calcium mass transfer using dialysate with a low calcium concentration (1.0 mM).

Lower dialysate calcium concentrations were recently proposed to overcome the risk of hypercalcemia in continuous ambulatory peritoneal dialysis (CAPD) patients on calcium-containing phosphate binders and/or vitamin D metabolites using the standard dialysate calcium concentration (SCa) of 1.75 mM. To assess transperitoneal calcium mass transfer (CaMT) in CAPD patients using a dialysate with a low calcium concentration (LCa, 1.00 mM), 18 stable patients were randomly allocated to receive either LCa or SCa. CaMT was assessed over 4 hours using 2L dialysate bags with three different dialysate glucose concentrations (1.5%, 2.3%, 4.25%). Total serum calcium (tCa), ionized calcium (iCa), and the exact dialysate volume were measured before and after the 4-hour dwell. A sample of the drained dialysate was obtained to measure the dialysate calcium concentration. The tCa and iCa levels were not significantly different in both groups prior to and did not change throughout the test. CaMT (median/range) was -0.64 mmol/exchange (-0.35(-)-1.29 mmol/exchange) using LCa with 1.5% glucose compared to 0.23 mmol (-0.18-0.87 mmol) with SCa (p < 0.0001). CaMT was negatively correlated to iCa and ultrafiltration volume [4.25%: LCa-1.22 (-0.84(-)-1.9); SCa -0.43 (-1.35-0.13); p < 0.001]. In summary, LCa results in a loss of calcium into the dialysate even at low ultrafiltration volumes and serum iCa levels. This might facilitate the prevention and therapy of renal osteodystrophy with calcium-containing phosphate binders and calcitriol. However, patients using LCa must be carefully monitored for calcium homeostasis and bone turnover.

Influence of retinol on human chondrocytes in agarose culture.

Vitamin A and its congeners, collectively called retinoids, are known to have teratogenic potential and have induced craniofacial and limb malformations in numerous animal species. More importantly, retinoids are recognized as teratogenic to fetuses of pregnant women who have taken such preparations for dermatologic disorders. Information gathered from the study of animal models suggests that retinoids interfere with cartilage differentiation. If chondrogenesis in limb development is disturbed it may contribute to limb reductions and malformations. In vitro studies using various animal systems have shown that cartilage matrix macromolecules are altered to resemble those secreted by mesenchymal cells. The response of human chondrocytes to retinoids in vitro is not known. Culture of human chondrocytes in agarose maintains the cartilage phenotype and therefore serves as a model system to evaluate the influence of retinoids directly on human chondrogenesis. The studies presented in this paper were done to determine if the expression of specific matrix macromolecules of human chondrocytes in agarose culture is altered by retinol treatment. Immunocytochemistry demonstrated enhanced labeling of type I collagen while type II collagen labeling was reduced in cultures treated with retinol. In addition, morphometric analyses indicated a decrease in the size and number of chondrogenic clusters and that individual cells synthesized less alcian blue matrix when compared to parallel control cultures. The size of the proteoglycan monomers, glycosaminoglycan side chains as well as the disaccharide composition were not affected. However, there was a reduction in the quantity of proteoglycan monomers produced.