Salt loading exacerbates diastolic dysfunction and cardiac remodeling in young female Ren2 rats

Abstract

Objective Recent data would suggest pre-menopausal insulin resistant women are more prone to diastolic dysfunction than men, yet it is unclear why. We and others have reported that transgenic (mRen2)27 (Ren2) rats overexpressing the murine renin transgene are insulin resistant due to oxidative stress in insulin sensitive tissues. As increased salt intake promotes inflammation and oxidative stress, we hypothesized that excess dietary salt would promote diastolic dysfunction in transgenic females under conditions of excess tissue Ang II and circulating aldosterone levels. Materials/methods For this purpose we evaluated cardiac function in young female Ren2 rats or age-matched Sprague-Dawley (SD) littermates exposed to a high (4%) salt or normal rat chow intake for three weeks. Results Compared to SD littermates, at 10 weeks of age, female Ren2 rats fed normal chow showed elevations in left ventricular (LV) systolic pressures, LV and cardiomyocyte hypertrophy, and displayed reductions in LV initial filling rate accompanied by increases in 3-nitrotyrosine content as a marker of oxidant stress. Following 3 weeks of a salt diet, female Ren2 rats exhibited no further changes in LV systolic pressure, insulin resistance, or markers of hypertrophy but exaggerated increases in type 1 collagen, 3-nitrotryosine content, and diastolic dysfunction. These findings occurred in parallel with ultrastructural findings of pericapillary fibrosis, increased LV remodeling, and mitochondrial biogenesis. Conclusion These data suggest that a diet high in salt in hypertensive female Ren2 rats promotes greater oxidative stress, maladaptive LV remodeling, fibrosis, and associated diastolic dysfunction without further changes in LV systolic pressure or hypertrophy.

Salt Loading Promotes Kidney Injury via Fibrosis in Young Female Ren2 Rats

“…Female Ren2 (6-7 weeks of age) and age-matched female Sprague-Dawley (SD) rats were randomly assigned to feed on normal chow (Ren2-C and SD-C, respectively) or chow containing 4% of salt (Ren2-HS and SD-HS, respectively) for 21 days [16]. …”

“…Transmission electron microscopy (TEM) images were captured as previously described [16,17]. Briefly, immediately after harvest, 1-2 mm of renal cortical tissues were placed in primary TEM fixative (2.5% of glutaraldehyde and 2.5% of paraformaldehyde).…”

“…3-Nitrotyrosine (3-NT) was quantified as previously described [16,17]. Briefly, 5 µm of paraffin-embedded kidney sections from different treatments were dewaxed, rehydrated, antigen retrieved and incubated overnight with 1:150 of primary rabbit polyclonal anti-3-NT antibody (Millipore).…”

“…Harvested kidney tissue was prepared as previously described [16,17]. Briefly, rehydrated paraffin-embedded sections were blocked in 5% of BSA, 5% of donkey serum and 0.01% of sodium azide in HEPES buffer for 4 h in a humidity chamber.…”

“…In order to address the effect of increased dietary salt intake on proteinuria and interstitial fibrosis in female rats, we utilized the transgenic Ren2 rat that overexpresses the mouse renin transgene and manifests elevated plasma aldosterone levels as well as increased kidney tissue Ang II. The female Ren2 rat exhibits normal body mass, but develops insulin resistance and hypertension, yet little proteinuria [12,15,16]. Therefore, to investigate the impact of increased dietary salt on the female kidney structure and function, we fed female Ren2 rats with a high-salt diet over 3 weeks and examined proteinuria along with structural abnormalities associated with progressive kidney disease.…”