Regulation of collecting duct AQP3 expression: response to mineralocorticoid

Abstract

Adrenocortical steroid hormones are importantly involved in the regulation of extracellular fluid volume. The present study was aimed at examining whether aldosterone and/or glucocorticoid regulates the abundance of aquaporin-3 (AQP3), -2, and -1 in rat kidney. In protocol 1, rats were adrenalectomized, followed by aldosterone replacement, dexamethasone replacement, or combined aldosterone and dexamethasone replacement (rats had free access to water but received a fixed amount of food). Protocol 2 was identical to protocol 1, except that all groups received fixed daily food and water intake. In both protocols 1 and 2, aldosterone deficiency was associated with increased fractional Na excretion and severe hyperkalemia. Semiquantitative immunoblotting revealed that aldosterone deficiency was associated with a dramatic downregulation of AQP3 abundance. Consistent with this, immunocytochemistry and immunoelectron microscopy revealed a marked decrease in AQP3 labeling in the basolateral plasma membranes of collecting duct principal cells. In contrast, AQP1 and AQP2 abundance and distribution were unchanged. Glucocorticoid deficiency revealed no changes in AQP3, -2, or -1 abundance. In protocol 3, Na restriction (to increase endogenous aldosterone levels) or exogenous aldosterone infusion in either normal rats or vasopressin-deficient Brattleboro rats was associated with a major increase in AQP3 abundance. In protocol 4, aldosterone levels were clamped by infusion of aldosterone, while Na intake was altered from a low to a high level. Under these circumstances, there were no changes in AQP3 or AQP2 abundance, although the level of the thiazidesensitive Na-Cl cotransporter was decreased. In conclusion, the results uniformly demonstrate that aldosterone regulates AQP3 abundance independently of Na intake. In contrast, changes in glucocorticoid levels in these models do not influence AQP3 or AQP2 abundance. Therefore, in the collecting duct aldosterone may regulate, at least in part, AQP3 expression in addition to regulating Na and K transport.adrenalectomy; aquaporin; glucocorticoid; mineralocorticoid; vasopressin RENAL REGULATION OF WATER and Na reabsorption or excretion is critical to the regulation of extracellular fluid (ECF) volume. Adrenocortical hormones, glucocorticoid and mineralocorticoid, are importantly involved in the normal modulation of renal water excretion and regulation of ECF volume (23,29,37,41,42). Therefore, chronic adrenal insufficiency with depletion of adrenocortical hormones is associated with altered water and Na metabolism (40), e.g., an inability to excrete a water load in glucocorticoid deficiency (18,19,24) or increased urinary flow and natriuresis in aldosterone deficiency (44). Moreover, elevated vasopressin and ANG II levels secondary to the altered ECF volume status (29, 41) may also contribute to the change in water balance, e.g., an impairment of free water clearance and dilutional hyponatremia (43). However, there is little information available regarding the selective effect of glu...

Distinct roles for the kidney and systemic tissues in blood pressure regulation by the renin-angiotensin system

“…At the time of the second nephrectomy and adrenalectomy, an osmotic minipump (ALZET model 2004; DURECT Corporation) containing aldosterone (A12930; Pfaltz & Bauer) and dexamethasone (D-1756; Sigma-Aldrich) was placed in a subcutaneous pouch. The doses of aldosterone (1 μg/day) and dexamethasone (1.2 μg/100 g body wt/d) were chosen to provide near-physiological replacement based on published studies (43,44). The aldosterone and dexamethasone were dissolved in polyethylene glycol 400 (Sigma-Aldrich) (45) and further diluted in normal saline.…”

Marinobufagenin Stimulates Fibroblast Collagen Production and Causes Fibrosis in Experimental Uremic Cardiomyopathy

“…7 These animals developed a similar degree of hypertension compared with PNx but were noted to have much lower plasma MBG and aldosterone levels, as well as substantially lower heart/weight body weight ratio compared with PNx alone (Table). Moreover, these animals subjected to PNx-ADx had almost no evidence for cardiac fibrosis based on trichrome staining or immunohistochemistry staining for collagen-1 or ␣ smooth muscle actin (see the online data supplement).…”

Erythropoietin Decreases Renal Fibrosis in Mice with Ureteral Obstruction

“…Kidney tissues from each experimental group were immersion-fixed with 4% paraformaldehyde in 0.1 M cacodylate buffer (pH 7.4) for 2 h. The immunolabeling was performed on the sections from paraffinembedded preparation (3-m thickness) using methods described previously in detail (29,30). The sections were incubated overnight at 4°C with primary antibodies against TGF-␤1 (1:500; Santa Cruz Biotechnology, Santa Cruz, CA), ␣-SMA (1:1000; Sigma, St. Louis, MO), or fibronectin (1:3000; BD Biosciences, Bedford, UK).…”