Aquaporin-2 excretion and renal function during the 1st week of life in preterm newborn infants.

In many preterm infants, a characteristic pattern of fluid and electrolyte homeostasis occurs during the 1st week of life, consisting of three phases: prediuretic, diuretic, and postdiuretic. In this study, we evaluated the possible role of aquaporin-2 (AQP2) in renal concentrating ability and correlated it with other markers of the renal function in healthy preterm infants. Daily urine and spot blood samples were collected from 9 healthy preterm (32 +/- 1 weeks) infants at postnatal ages 1, 3, and 7 days. Urine and serum osmolality, creatinine, electrolytes, and AQP2 excretion were measured. All infants showed a significant (about 7%) weight loss on day 3 associated with a more than threefold increase in urine output without a significant change in fluid intake (diuretic phase). The creatinine clearance increased on day 3, indicating an increase in glomerular filtration rate. Interestingly, on day 3, the level of total excreted AQP2 (pmol/h) was significantly higher when compared to day 1 and day 7, and the same tendency was observed for urine osmolality. To conclude, the observed increase in urine osmolality and creatinine clearance during the diuretic phase, paralleled by an increase in total AQP2 excretion, suggests that AQP2 can contribute to the urinary concentrating ability early in postnatal life.

Effects of intermittent administration of pamidronate on the mechanical properties of canine cortical and trabecular bone.

The mechanical properties of cortical and trabecular bones from beagles treated with the bisphosphonate pamidronate (administered intermittently 1 week every month for 3 months, at a dosage of 0.45 mumol/kg/day) were assessed. The mechanical properties of cortical bone were measured by four-point bending tests on femoral quadrants, in order to measure their elastic modulus and ultimate stress. The structural properties of whole tibias were measured in torsion to determine the torsional stiffness and failure torque. The elastic modulus and maximum compressive stress of the trabecular bone samples were measured by compression tests of trabecular cores. Intermittent treatment with pamidronate did not change the pattern of mechanical properties that occurs naturally around the femur or the torsional stiffness and failure torque of the tibias. By contrast, pamidronate did significantly increase the modulus of elasticity (by 19%) and maximum compressive stress (by 33%) of vertically aligned cylindrical trabecular specimens taken from the vertebrae of the beagles.

Effect of pamidronate on the mechanical properties of canine bone.

Pamidronate (Aredia) has been used in the treatment of hypercalcemia of malignancy, in Paget's disease of bone, and in osteoporosis to prevent bone resorption. In a 3-month study, intermittent intravenous infusions of pamidronate in dogs did not change the mechanical properties of cortical bone, either in torsion or bending. However, such treatment increased the compressive stiffness and torsional strength of trabecular specimens taken from vertebrae. In a 1-year study, oral administration of pamidronate at various doses produced a linear increase in the elastic modulus of trabecular bone with the square root of the dose and no change in cortical bone. Finally, in a 2-year study (1 year on pamidronate followed by 1 year recovery), no differences were found in the mechanical properties of whole bone whatever dose was given.

Changes in bone mineralization, architecture and mechanical properties due to long-term (1 year) administration of pamidronate (APD) to adult dogs.

The goal of this study was to evaluate the effect of 1 year of APD administration on bone mineralization and bone mineral chemistry in the dog. Disodium pamidronate (APD) was given orally by gavage to mature beagle dogs at doses of 0, 2.5, 12.5 and 25.0 mg/kg per day (0.1% concentration for 12 months) as part of a long-term toxicity study. The os ilium and a vertebra were used to determine the mineralization profile and, subsequently, each density fraction was analysed chemically. The ribs were used to determine lattice parameters of the apatite crystal size using X-ray diffraction. The sternum was used to determine selected morphometric parameters using image analysis of specimen X-ray films and subsequently to determine mechanical properties using velocity-of-sound techniques. We found that for both the ilium and the vertebrae there was a significant shift of the mineralization profile towards greater density in a dose-related manner. This effect levelled off with the highest dose because the shift in mineralization profile correlated better with the square root of the dose than with the dose. Together with data on crystal size, which show an increase in lattice parameters and a decrease in crystal size with dose, our data lead us to believe that long-term administration of APD leads to an increase in bone mineralization without major changes in bone chemistry of Ca, Mg, and P and with a decrease in bone apatite crystal size. The image analysis shows a dose-related increase in trabecular bone volume and thickness.(ABSTRACT TRUNCATED AT 250 WORDS)