Restoration of afferent arteriolar autoregulatory behavior in ischemia-reperfusion injury in rat kidneys.

Renal autoregulation is critical in maintaining stable renal blood flow (RBF) and glomerular filtration rate (GFR). Renal ischemia-reperfusion (IR)-induced kidney injury is characterized by reduced RBF and GFR. The mechanisms contributing to renal microvascular dysfunction in IR have not been fully determined. We hypothesized that increased reactive oxygen species (ROS) contributed to impaired renal autoregulatory capability in IR rats. Afferent arteriolar autoregulatory behavior was assessed using the blood-perfused juxtamedullary nephron preparation. IR was induced by 60 min of bilateral renal artery occlusion followed by 24 h of reperfusion. Afferent arterioles from sham rats exhibited normal autoregulatory behavior. Stepwise increases in perfusion pressure caused pressure-dependent vasoconstriction to 65 ± 3% of baseline diameter (13.2 ± 0.4 µm) at 170 mmHg. In contrast, pressure-mediated vasoconstriction was markedly attenuated in IR rats. Baseline diameter averaged 11.7 ± 0.5 µm and remained between 90% and 101% of baseline over 65-170 mmHg, indicating impaired autoregulatory function. Acute antioxidant administration (tempol or apocynin) to IR kidneys for 20 min increased baseline diameter and improved autoregulatory capability, such that the pressure-diameter profiles were indistinguishable from those of sham kidneys. Furthermore, the addition of polyethylene glycol superoxide dismutase or polyethylene glycol-catalase to the perfusate blood also restored afferent arteriolar autoregulatory responsiveness in IR rats, indicating the involvement of superoxide and/or hydrogen peroxide. IR elevated mRNA expression of NADPH oxidase subunits and monocyte chemoattractant protein-1 in renal tissue homogenates, and this was prevented by tempol pretreatment. These results suggest that ROS accumulation, likely involving superoxide and/or hydrogen peroxide, impairs renal autoregulation in IR rats in a reversible fashion.NEW & NOTEWORTHY Renal ischemia-reperfusion (IR) leads to renal microvascular dysfunction manifested by impaired afferent arteriolar autoregulatory efficiency. Acute administration of scavengers of reactive oxygen species, polyethylene glycol-superoxide dismutase, or polyethylene glycol-catalase following renal IR restored afferent arteriolar autoregulatory capability in IR rats, indicating that renal IR led to reversible impairment of afferent arteriolar autoregulatory capability. Intervention with antioxidant treatment following IR may improve outcomes in patients by preserving renovascular autoregulatory function and potentially preventing the progression to chronic kidney disease after acute kidney injury.

Loss of circadian gene Bmal1 in the collecting duct lowers blood pressure in male, but not female, mice.

Kidney function follows a 24-h rhythm subject to regulation by circadian genes including the transcription factor Bmal1. A high-salt diet induces a phase shift in Bmal1 expression in the renal inner medulla that is dependent on endothelin type B (ETB) receptors. Furthermore, ETB receptor-mediated natriuresis is sex dependent. Therefore, experiments tested the hypothesis that collecting duct Bmal1 regulates blood pressure in a sex-dependent manner. We generated a mouse model that lacks Bmal1 expression in the collecting duct, where ETB receptor abundance is highest. Male, but not female, collecting duct Bmal1 knockout (CDBmal1KO) mice had significantly lower 24-h mean arterial pressure (MAP) than flox controls (105 ± 2 vs. 112 ± 3 mmHg for male mice and 106 ± 1 vs. 108 ± 1 mmHg for female mice, by telemetry). After 6 days on a high-salt (4% NaCl) diet, MAP remained significantly lower in male CDBmal1KO mice than in male flox control mice (107 ± 2 vs. 113 ± 1 mmHg), with no significant differences between genotypes in female mice (108 ± 2 vs. 109 ± 1 mmHg). ETB receptor blockade for another 6 days increased MAP similarly in both male and female CDBmal1KO and flox control mice. However, MAP remained lower in male CDBmal1KO mice than in male flox control mice (124 ± 2 vs. 130 ± 2 mmHg). No significant differences were observed between female CDBmal1KO and flox mice during ETB blockade (130 ± 2 vs. 127 ± 2 mmHg). There were no significant genotype differences in amplitude or phase of MAP in either sex. These data suggest that collecting duct Bmal1 has no role in circadian MAP but plays an important role in overall blood pressure in male, but not female, mice.

Early life stress induces immune priming in kidneys of adult male rats.

Early life stress (ELS) in humans is associated with elevated proinflammatory markers. We hypothesized that ELS induces activation of the immune response in a rat model of ELS, maternal separation (MatSep), in adulthood. MatSep involves separating pups from the dam from postnatal day 2 to postnatal day 14 for 3 h/day. Control rats are nonseparated littermates. We determined circulating and renal immune cell numbers, renal immune cell activation markers, renal cytokine levels, and the renal inflammatory gene expression response to low-dose lipopolysaccharide (LPS) in male MatSep and control rats. We observed that MatSep did not change the percentage of gated events for circulating CD3+, CD4+, CD8+, and CD4+/Foxp3+ cells or absolute numbers of mononuclear and T cells in the circulation and kidneys; however, MatSep led to an increase in activation of renal neutrophils as well as CD44+ cells. Renal toll-like receptor 4 (TLR4) and interleukin 1 beta (IL-1ß) was significantly increased in MatSep rats, specifically in the outer and inner medulla and distal nephron, respectively. Evaluation of renal inflammatory genes showed that in response to a low-dose LPS challenge (2 mg/kg iv) a total of 20 genes were significantly altered in kidneys from MatSep rats (17 genes were upregulated and 3 were downregulated), as opposed to no significant differences in gene expression in control vs. control + LPS groups. Taken together, these findings indicate that MatSep induces priming of the immune response in the kidney.

Maternal separation enhances anticontractile perivascular adipose tissue function in male rats on a high-fat diet.

Clinical studies have shown that obesity negatively impacts large arteries' function. We reported that rats exposed to maternal separation (MatSep), a model of early life stress, display enhanced angiotensin II (ANG II)-induced vasoconstriction in aortic rings cleaned of perivascular adipose tissue (PVAT) under normal diet (ND) conditions. We hypothesized that exposure to MatSep promotes a greater loss of PVAT-mediated protective effects on vascular function and loss of blood pressure (BP) rhythm in rats fed a high-fat diet (HFD) when compared with controls. MatSep was performed in male Wistar-Kyoto rats from days 2 to 14 of life. Normally reared littermates served as controls. On ND, aortic rings from MatSep rats with PVAT removed showed increased ANG II-mediated vasoconstriction versus controls; however, rings from MatSep rats with intact PVAT displayed blunted constriction. This effect was exacerbated by an HFD in both groups; however, the anticontractile effect of PVAT was greater in MatSep rats. Acetylcholine-induced relaxation was similar in MatSep and control rats fed an ND, regardless of the presence of PVAT. HFD impaired aortic relaxation in rings without PVAT from MatSep rats, whereas the presence of PVAT improved relaxation in both groups. On an HFD, immunolocalization of vascular smooth muscle-derived ANG-(1-7) and PVAT-derived adiponectin abundances were increased in MatSep. In rats fed an HFD, 24-h BP and BP rhythms were similar between groups. In summary, MatSep enhanced the ability of PVAT to blunt the heightened ANG II-induced vasoconstriction and endothelial dysfunction in rats fed an HFD. This protective effect may be mediated via the upregulation of vasoprotective factors within the adipovascular axis.

Acclimation to a High-Salt Diet Is Sex Dependent.

Background Premenopausal women are less likely to develop hypertension and salt-related complications than are men, yet the impact of sex on mechanisms regulating Na+ homeostasis during dietary salt challenges is poorly defined. Here, we determined whether female rats have a more efficient capacity to acclimate to increased dietary salt intake challenge. Methods and Results Age-matched male and female Sprague Dawley rats maintained on a normal-salt (NS) diet (0.49% NaCl) were challenged with a 5-day high-salt diet (4.0% NaCl). We assessed serum, urinary, skin, and muscle electrolytes; total body water; and kidney Na+ transporters during the NS and high-salt diet phases. During the 5-day high-salt challenge, natriuresis increased more rapidly in females, whereas serum Na+ and body water concentration increased only in males. To determine if females are primed to handle changes in dietary salt, we asked the question whether the renal endothelin-1 natriuretic system is more active in female rats, compared with males. During the NS diet, female rats had a higher urinary endothelin-1 excretion rate than males. Moreover, Ingenuity Pathway Analysis of RNA sequencing data identified the enrichment of endothelin signaling pathway transcripts in the inner medulla of kidneys from NS-fed female rats compared with male counterparts. Notably, in human subjects who consumed an Na+-controlled diet (3314-3668 mg/day) for 3 days, women had a higher urinary endothelin-1 excretion rate than men, consistent with our findings in NS-fed rats. Conclusions These results suggest that female sex confers a greater ability to maintain Na+ homeostasis during acclimation to dietary Na+ challenges and indicate that the intrarenal endothelin-1 natriuretic pathway is enhanced in women.

Transepithelial D-glucose and D-fructose transport across the American lobster, Homarus americanus, intestine.

Transepithelial transport of dietary D-glucose and d-fructose was examined in the lobster Homarus americanus intestine using D-[(3)H]glucose and D-[(3)H]fructose. Lobster intestines were mounted in a perfusion chamber to determine transepithelial mucosal to serosal (MS) and serosal to mucosal (SM) transport mechanisms of glucose and fructose. Both MS glucose and fructose transport, as functions of luminal sugar concentration, increased in a hyperbolic manner, suggesting the presence of mucosal transport proteins. Phloridizin inhibited the MS flux of glucose, but not that of fructose, suggesting the presence of a sodium-dependent (SGLT1)-like glucose co-transporter. Immunohistochemical analysis, using a goat anti-rabbit GLUT5 polyclonal antibody, revealed the localization of a brush border GLUT5-like fructose transport protein. MS fructose transport was decreased in the presence of mucosal phloretin in warm spring/summer animals, but the same effect was not observed in cold autumn/winter animals, suggesting a seasonal regulation of sugar transporters. Mucosal phloretin had no effect on MS glucose transport. Both SM glucose and SM fructose transport were decreased in the presence of increasing concentrations of serosal phloretin, providing evidence for the presence of a shared serosal GLUT2 transport protein for the two sugars. The transport of d-glucose and d-fructose across lobster intestine is similar to sugar uptake in mammalian intestine, suggesting evolutionarily conserved absorption processes for these solutes.

Evidence for G-Protein-Coupled Estrogen Receptor as a Pronatriuretic Factor.

Background The novel estrogen receptor, G-protein-coupled estrogen receptor (GPER), is responsible for rapid estrogen signaling. GPER activation elicits cardiovascular and nephroprotective effects against salt-induced complications, yet there is no direct evidence for GPER control of renal Na+ handling. We hypothesized that GPER activation in the renal medulla facilitates Na+ excretion. Methods and Results Herein, we show that infusion of the GPER agonist, G1, to the renal medulla increased Na+ excretion in female Sprague Dawley rats, but not male rats. We found that GPER mRNA expression and protein abundance were markedly higher in outer medullary tissues from females relative to males. Blockade of GPER in the renal medulla attenuated Na+ excretion in females. Given that medullary endothelin 1 is a well-established natriuretic factor that is regulated by sex and sex steroids, we hypothesized that GPER activation promotes natriuresis via an endothelin 1-dependent pathway. To test this mechanism, we determined the effect of medullary infusion of G1 after blockade of endothelin receptors. Dual endothelin receptor subtype A and endothelin receptor subtype B antagonism attenuated G1-induced natriuresis in females. Unlike males, female mice with genetic deletion of GPER had reduced endothelin 1, endothelin receptor subtype A, and endothelin receptor subtype B mRNA expression compared with wild-type controls. More important, we found that systemic GPER activation ameliorates the increase in mean arterial pressure induced by ovariectomy. Conclusions Our data uncover a novel role for renal medullary GPER in promoting Na+ excretion via an endothelin 1-dependent pathway in female rats, but not in males. These results highlight GPER as a potential therapeutic target for salt-sensitive hypertension in postmenopausal women.

Childhood adversity and mechanistic links to hypertension risk in adulthood.

Adverse childhood experiences (ACEs), defined as traumatic events in childhood that range from various forms of abuse to household challenges and dysfunction, have devastating consequences on adult health. Epidemiological studies in humans and animal models of early life stress (ELS) have revealed a strong association and insight into the mechanistic link between ACEs and increased risk of cardiovascular disease (CVD). This review focuses on the mechanistic links of ACEs in humans and ELS in mice and rats to vasoactive factors and immune mediators associated with CVD and hypertension risk, as well as sex differences in these phenomena. Major topics of discussion in this review are as follows: (a) epidemiological associations between ACEs and CVD risk focusing on hypertension, (b) evidence for association of ACE exposures to immune-mediated and/or vasoactive pathways, (c) rodent models of ELS-induced hypertension risk, (d) proinflammatory mediators and vasoactive factors as mechanisms of ELS-induced hypertension risk. We also provide some overall conclusions and directions of further research. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

K⁺-dependent ³H-D-glucose transport by hepatopancreatic brush border membrane vesicles of a marine shrimp.

The effects of sodium, potassium, sugar inhibitors, and membrane potential on ³H-D-glucose uptake by hepatopancreatic epithelial brush border membrane vesicles (BBMV) of the Atlantic marine shrimp, Litopenaeus setiferus, were investigated. Brush border membrane vesicles were prepared using a MgCl2/EGTA precipitation method and uptake experiments were conducted using a high speed filtration technique. ³H-D-Glucose uptake was stimulated by both sodium and potassium and these transport rates were almost doubled in the presence of an inside-negative-induced membrane potential. Kinetics of ³H-D-glucose influx were hyperbolic functions of both external Na⁺ or K⁺, and an induced membrane potential increased influx J(max) and lowered K(m) in both salts. ³H-D-Glucose influx versus [glucose] in both Na⁺ or K⁺ media also displayed Michaelis-Menten properties that were only slightly affected by induced membrane potential. Phloridzin was a poor inhibitor of 0.5 mM ³H-D-glucose influx, requiring at least 5 mM in NaCl and 10 mM in KCl to significantly reduce hexose transport. Several sugars (D-galactose, α-methyl-D-gluco-pyranoside, unlabeled D-glucose, D-fructose, and D-mannose) were used at 75 mM as potential inhibitors of 0.1 mM ³H-D-glucose influx. Only unlabeled D-glucose, D-fructose, and D-mannose significantly (p < 0.05) reduced labeled glucose transport. An additional experiment using increasing concentrations of D-mannose (0, 10, 25, 75, and 100 mM) showed this hexose to be an effective inhibitor of 0.1 mM ³H-D-glucose uptake at concentrations of 75 mM and higher. As a whole these results suggest that ³H-D-glucose transport by hepatopancreatic BBMV occurs by a carrier system that is able to use both Na⁺ and K⁺ as drivers, is enhanced by membrane potential, is relatively refractory to phloridzin, and is only inhibited by itself, D-fructose, and D-mannose. These properties are similar to those exhibited by the mammalian SLC5A9/SGLT4 transporter, suggesting that an invertebrate analogue of this protein may occur in shrimp.