Sex differences in adaptive downregulation of pre-macula densa sodium transporters with ANG II infusion in mice.

An increase in blood pressure (BP) due to angiotensin II (ANG II) infusion or other means is associated with adaptive pressure natriuresis due to reduced sodium reabsorption primarily in proximal tubule (PT) and thick ascending limb (TAL). We tested the hypothesis that male and female mice would show differential response to ANG II infusion with regard to the regulation of the protein abundance of sodium transporters in the PT and TAL and that these responses would be modulated by aging. Young (approximately 3 mo) and old (approximately 21 mo) male and female mice were infused with ANG II at 800 ng x kg body wt(-1) x min(-1) by osmotic minipump for 7 days or received a sham operation. ANG II increased mean arterial pressure (MAP), measured by radiotelemetry, significantly more in male mice of both ages (increased approximately 30-40 mmHg), compared with females (increased approximately 15-25 mmHg). On day 1, MAP was also significantly increased in old mice, relative to young (P = 0.01). ANG II infusion was associated with a significant decline in plasma testosterone (to <30% of control male) in male mice and rise in young female mice (to 478% of control female). No sex differences were found in the upregulation of the sodium hydrogen exchanger abundance on Western blots observed with ANG II infusion or the downregulation of the sodium phosphate cotransporter; however, aging did impact on some of these changes. Male mice (especially young) also had significantly reduced levels of the TAL bumetanide-sensitive Na-K-2Cl cotransporter (to 60% of male control), while young females showed an increase (to 126% of female control) with ANG II infusion. These sex differences do not support impaired pressure natriuresis in male mice, but might reflect a greater need and attempt to mount an appropriately BP-metered natriuretic response by additional downregulation of TAL sodium reabsorption.

Sex and age result in differential regulation of the renal thiazide-sensitive NaCl cotransporter and the epithelial sodium channel in angiotensin II-infused mice.

BACKGROUND/AIMS: We determined the effects of age and sex on the blood pressure (BP) response to angiotensin II (Ang II) infusion and evaluated the potential mechanistic role of the thiazide-sensitive NaCl cotransporter (NCC) and the epithelial sodium channel (ENaC). METHODS: Male and female mice (approximately 3 or 21 months of age) were infused with Ang II or control for 7 days. RESULTS: Males had a greater BP response to Ang II, somewhat enhanced by aging. Mean systolic BPs (at 7 days) were (mm Hg): 161, 143, 172, and 157 in young male, young female, old male, and old female mice, respectively. Immunoblotting changes in the whole kidney that supported this BP profile included a 51 and 52% increase in NCC band density in the old females and old males (as compared to sex-respective controls) with Ang II infusion, while the young males and young females showed an increase of 40 and 0%, respectively. Young males also had a greater reduction in major bands of beta- and gamma-ENaC, than did young female mice. The natriuretic response to hydrochlorothiazide supported an increase in activity of NCC with Ang II in aged mice only. CONCLUSIONS: Increased sensitivity to Ang II in aging and male mice may involve overactivity of NCC.

Trafficking of ENaC subunits in response to acute insulin in mouse kidney.

Studies done in cell culture have demonstrated that insulin activates the epithelial sodium channel (ENaC) via a variety of mechanisms. However, to date, upregulation of ENaC in native renal tissue by in vivo administration of insulin has not been demonstrated. To address this, we injected 6-mo-old male C57BL/CBA mice (n = 14/group) intraperitoneally with vehicle or 0.5 U/kg body wt insulin and examined short-term (1-2 h) sodium excretion and kidney ENaC subunits (alpha, beta, and gamma) and serum and glucocorticoid-induced kinase (SGK-1) regulation. Insulin resulted in a significant reduction in urine sodium (by approximately 80%) that was restored by intraperitoneal administration of the ENaC antagonist, benzamil (1.4 mg/kg body wt). Differential centrifugation followed by Western blotting of whole kidney revealed significantly increased band densities (by 26-103%) for insulin- relative to vehicle-treated mice for alpha- and gamma-ENaC in the homogenate (H), and plasma membrane-enriched fraction (MF), with no difference in the vesicle-enriched fraction (VF). Similarly, beta-ENaC was significantly increased in MF (by 45%) but no change in the H. It was, however, significantly decreased in the VF (by 28%) with insulin. In agreement, immunoperoxidase labeling demonstrated relatively stronger apical, relative to cytosolic, localization of alpha-, beta-, and gamma-ENaC with insulin, whereas, with vehicle, labeling was fairly evenly dispersed throughout collecting duct principal cells. Furthermore, Western blotting showed insulin increased SGK-1 (by 75%) and phosphorylated-SGK band densities (by 30%) but only in the MF. These studies demonstrate novel in vivo regulation of renal ENaC activity and subunit proteins and SGK-1 by insulin in the acute time frame in the mouse.