Effect of pregnancy, postnatal growth, and gender on renal sulfate transport

Serum sulfate concentrations are increased in infants, young children, and pregnant women, compared with adult values. The objective of this investigation was to examine the influences of age, gender, and pregnancy on renal sulfate transport using guinea pigs as an animal model. Membrane vesicles were isolated from the kidney cortex of male animals at four different ages, from male and female adult animals, and from pregnant and nonpregnant female animals. There were no significant differences in marker enzymes for the brush-border membrane (BBM) or basolateral membrane (BLM) among all groups examined. Uptake was determined by a rapid filtration method and membrane fluidity by measuring the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene. The V(max) values for Na⁺/sulfate cotransport in BBM were significantly increased with decreasing age, whereas the K(m) for this process was unchanged. The V(max) and K(m) for Na⁺/sulfate co-tranSport in BBM of pregnant animals were significantly higher than the values in the nonpregnant group. Bicarbonate-driven anion exchange of sulfate in BLM was not different among the different age groups. The V(max) for the bicarbonate/sulfate exchange process in BLM was not different between pregnant and nonpregnant groups; however, the K(m) for this process in BLM of pregnant animals was significantly greater than the value in nonpregnant animals. There were no gender-related differences in sulfate transport in BBM or BLM isolated from adult male and female animals. Renal BBM fluidity was increased with decreasing age and in pregnant animals, suggesting that altered membrane fluidity may represent one possible mechanism to explain the increased sodium/sulfate uptake in young and pregnant animals. The higher V(max) for Na⁺/sulfate co-transport in young and pregnant animals suggests that there is an increased density of co-transporter protein or an increase in the rate of movement of the carrier protein (i.e., turnover) once loaded with sodium and sulfate. This increased conservation of inorganic sulfate in young and pregnant guinea pigs may be related to the increased demand for sulfated substrates, such as sulfated glycosaminoglycans, during growth and development.