Aquaporin-2 is detectable in the urine, and changes in the urinary excretion of this protein can be used as an index of the action of vasopressin on the kidney.

These results suggest that rabphilin-3A is a major autoantigen in LINH. Autoantibodies to rabphilin-3A may serve as a biomarker for the diagnosis of LINH and be useful for the differential diagnosis in patients with CDI.

We determined alterations in renal aquaporin-2 (AQP2) gene expression in association with impaired water excretion in glucocorticoid-deficient rats. After adrenalectomy, Sprague-Dawley rats were administered aldosterone alone by osmotic pumps (glucocorticoid-deficient rats). As a control, both aldosterone and dexamethasone were administered. These animals were subjected to the studies on days 7-14. The expressions of AQP2 mRNA and protein in kidney of the glucocorticoid-deficient rats were increased by 1.6- and 1.4-fold compared with the control rats, respectively. An acute oral water load test verified the marked impairment in water excretion in the glucocorticoid-deficient rats. One hour after the water load, the expressions of AQP2 mRNA and protein were significantly reduced in the control rats, but they remained unchanged in the glucocorticoid-deficient rats. However, there was no alteration in [(3)H]arginine vasopressin (AVP) receptor binding and AVP V(2) receptor mRNA expression in the glucocorticoid-deficient rats. A V(2)-receptor antagonist abolished the increased expressions of AQP2 mRNA and protein in the glucocorticoid-deficient rats. These results indicate that augmented expression of AQP2 participates in impaired water excretion, dependent on AVP, in glucocorticoid deficiency.

The present study was undertaken to determine whether urinary excretion of aquaporin-2 (AQP-2) participates in the involvement of arginine vasopressin (AVP) in hyponatremia less than 130 mmol/L in 33 elderly subjects (> or =65 yr old) during the last 5-yr period. Subjects were separated into euvolemic hyponatremia groups: 13 with hypopituitarism, 8 with syndrome of inappropriate secretion of antidiuretic hormone (SIADH), 8 with mineralocorticoid-responsive hyponatremia of the elderly, and 4 with miscellaneous diseases. Approximately 40% of those with hyponatremia was derived from hypopituitarism, but severe hyponatremia was found in the patients with SIADH and mineralocorticoid-responsive hyponatremia of the elderly. Plasma AVP levels remained relatively high despite hypoosmolality and were tightly linked with exaggerated urinary excretion of AQP-2 and antidiuresis in the 3 groups of patients, except for one miscellaneous one. An acute water load test verified the impairment in water excretion, because the percent excretion of the water load was less than 42% and the minimal urinary osmolality was not sufficiently diluted. Also, plasma AVP and urinary excretion of AQP-2 were not reduced after the water load. The inappropriate secretion of AVP was evident in the patients with SIADH and hypopituitarism, and hydrocortisone replacement normalized urinary excretion of AQP-2 and renal water excretion in those with hypopituitarism. In contrast, the appropriate antidiuresis seemed to compensate loss of body fluid in the patients with mineralocorticoid-responsive hyponatremia of the elderly, who lost circulatory blood volume by 7.3% (mean). Fludrocortisone acetate increased renal sodium handling and body fluid, resulting in the reduction in AVP release and urinary excretion of AQP-2 in mineralocorticoid-responsive hyponatremia of the elderly. These findings indicate that urinary excretion of AQP-2 may be a more sensitive measure of AVP effect on renal collecting duct cells than are plasma AVP levels, and that increased urinary excretion of AQP-2 shows exaggerated AVP-induced antidiuresis in hyponatremic subjects in the elderly. In addition, mineralocorticoid-responsive hyponatremia of the elderly has to be carefully differentiated from SIADH in elderly subjects.

The early atherosclerotic lesion is characterized by the migration of inflammatory cells, including monocytes, which may serve as a source of cytokines such as monocyte chemoattractant protein 1 (MCP-1), a homologue of mouse JE. We investigated the effect of MCP-1 on the growth of vascular smooth muscle cells (VSMC) isolated from rat aortae. In Northern blot analysis, MCP-1/JE transcripts were not observed in unstimulated VSMC, but its expression was clearly observed by exposure to lipopolysaccharide (1 micrograms/ml) for 6 h. Human recombinant MCP-1 inhibited the uptake of [3H]thymidine by VSMC cultured in 0.5% fetal bovine serum (FBS) containing Dulbecco's modified Eagle's medium (DMEM) in a dose-dependent manner. The inhibitory effect of MCP-1 on the growth of VSMC was also confirmed by a change in cell counts. The antiproliferative effect of MCP-1 was significantly blocked in the presence of an anti-MCP-1 antibody. MCP-1-induced inhibition of [3H]thymidine uptake was not affected in the presence of indomethacin (1 micrograms/ml) or NG-monomethyl-L-arginine (0.1 mM), and MCP-1 showed no effect on 6-ketoprostaglandin F1 alpha, guanosine 3',5'-cyclic monophosphate, and adenosine 3',5'-cyclic monophosphate syntheses in VSMC. These results indicate that MCP-1 inhibits the proliferation of VSMC in vitro and that its effect is independent of prostaglandin or nitric oxide generation.