Aquaporin-1 expression in proximal tubule epithelial cells of human kidney is regulated by hyperosmolarity and contrast agents

Primary cells of renal proximal tubule epithelium (S1 segment) of human kidney (HRPTE cells) up-regulate aquaporin-1 (AQP-1) expression in response to hyperosmolarity. NaCl and D(+)-raffinose increased (2-2.5 fold) AQP-1 expression when medium osmolarity was 400 and 500 mOsm/kg.H2O. Urea did not have this effect. Unlike our previous findings with mIMCD-3 cells, vasopressin (10(-8)M) did not affect AQP-1 expression in HRPTE cells in isosmolar or NaCl-enriched hyperosmolar conditions. Furthermore, HRPTE cells increased (3-4 fold) AQP-1 expression when exposed to hyperosmolar Reno-60 and Hypaque-76 (diatrizoates, ionic) contrast agents at 400 and 500 mOsm/kg.H2O. Isosmolar (290 mOsm/kg H2O) Visipaque (iodixanol, non-ionic) at 10% (v/v) concentrations also increased AQP-1 expression, and 25% v/v of Visipaque rendered morphological alterations of HRPTE cells and a 3-fold increase in AQP-1 expression after 24h exposure. Finally, semi-quantitative RT-PCR of HRPTE cells subjected to various isosmolar or hyperosmolar conditions demonstrated up-regulation of AQP-1 mRNA and protein levels. Our results suggest AQP-1 up-regulation in HRPTE cells exposed to environmental stresses such as hyperosmolarity and high doses of isosmolar contrast agents.

Nutritional implications of recombinant human erythropoietin therapy in renal disease

The treatment of anemia in patients with renal failure has been dramatically changed with the development of recombinant human erythropoietin (r-HuEPO). This review discusses the pathogenesis of the anemia renal failure and the biology of erythropoietin. Causes of poor response to r-HuEPO therapy are outlined, and the importance of adequate available iron is highlighted. Parameters used to measure iron adequacy include serum iron levels, transferrin saturation, and ferritin levels. Other nutritional deficiencies, such as folic acid and vitamin B-12, can also impair r-HuEPO response. Clearly, the advent of r-HuEPO treatment for patients with renal failure and anemia has brought another dimension to the care of these patients. Optimal nutrition management is critical for the success of this new agent.

Hormonal response to exercise in high altitude natives and COPD patients

Plasma renin activity (PRA) and aldosterone increase with exercise. Acute hypoxia interferes with this hormonal response to exercise, but the effects of chronic or intermittent hypoxia on exercise-induced hormonal changes are not well understood. The hormonal response to exercise was studied in two groups of subjects who were expected to become hypoxic during exercise (high altitude natives at high altitude and patients with moderate to severe chronic obstructive pulmonary disease or COPD), and normal controls. Both the high altitude natives and COPD patients became hypoxic with maximal exercise. The rate of rise of PRA and epinephrine was significantly less in the two study groups than the normal subjects. Changes in aldosterone levels with exercise were similar to PRA but the differences among groups were not significant. Differences between the groups were not seen for changes in atrial natriuretic polypeptide and norepinephrine during exercise. These results support the concept that hypoxia interferes with the renin-aldosterone and adrenal medullary response to exercise.