Renal tubular reabsorption of inorganic sulfate is greater in younger than older guinea pigs. To determine the mechanism of this difference, we studied the transport of inorganic sulfate in renal brush border membrane vesicles (BBMV) obtained from young (< 25 days) and adult guinea pigs (> 60 days). BBMV were obtained by mechanical and osmotic disruption of dissected renal cortices followed by magnesium precipitation and differential centrifugation. After the membranes were incubated for 10 s in solutions containing inorganic sulfate at several concentrations (0.1-10 mM) and trace amounts of 35sulfate, intravesicular uptake was measured. Based on 35sulfur uptake, reabsorption transport kinetics (Vmax and Km) were estimated. BBMV obtained from young guinea pigs demonstrated higher sodium-sulfate cotransport, Vmax (51.79 +/- 4.34 pmol/mg protein per s) than those obtained from adult animals (Vmax = 34.28 +/- 9.17 pmol/mg per s), P < 0.05. Vmax values are represented as means plus or minus standard deviation. No differences in Km were observed. Our results indicate that age-related differences in renal inorganic sulfate reabsorption are due to a higher Vmax for sodium-sulfate cotransport in the younger animals, suggesting a higher density of sodium-sulfate cotransporters or an increased cotransport turnover rate in this age group.

Renal adaptation to changes in inorganic sulfate intake and age was studied by comparing sulfate uptake by proximal tubule brush border membrane vesicles (BBMV) from guinea pigs of different ages on relatively high- or low-sulfate diets. Adult (> 60 days) or young guinea pigs (< 25 days) were fed either a control diet (0.28% sulfur content), a sulfur-free diet, or a high-sulfate diet. After 5 days on the diet, BBMV were obtained and kinetic analysis of 35sulfate uptake was determined. In adult guinea pigs, the low-sulfate diet produced a significant increase in apparent maximal velocity (Vmax). In young guinea pigs, a lower sulfate intake did not appreciably increase Vmax, but a high-sulfate intake produced a reduction in Vmax. The affinity for sulfate (Km) was not changed in either age group. The dietary sulfate intake did not alter sodium gradient dependent-D-glucose or 32phosphate Vmax. In conclusion, our data indicate that renal inorganic sulfate BBMV uptake is regulated and responds to conditions of increased need (i.e., during the growth phase in young animals and during periods of decreased sulfate availability in adult animals) by increasing BBMV Vmax.

Melorheostosis is a benign, rare, congenital disorder of hyperostosis of one or more bones. In this report, we describe a 5-year-old girl with melorheostosis of the left iliac wing, femur, and tibia who developed severe hypertension secondary to left renal artery stenosis. Numerous soft tissue and vascular anomalies have been reported in patients with melorheostosis. To our knowledge this is the first case where renal artery stenosis has been associated with melorheostosis. Several hypotheses for bone and vascular involvement in melorheostosis are reviewed.