Loop Diuretic Resistance in a Mouse Model of Cardiorenal Syndrome
Authors: Baiden Isaac , Mendez Mariela , Xu Jiang , Liao Tang-Dong , Maskey Dipak , Ortiz Pablo 
Published: May 2024

Nearly 30% of patients with heart failure (HF) develop Cardiorenal syndrome type 2 (CRS2), characterized by renal injury and lower glomerular filtration rate (GFR) secondary to lower cardiac function. Patients with uncompensated heart failure develop edema and are usually treated with a loop diuretic, such as furosemide, that acts in thick ascending limb (TAL) to inhibit NKCC2. However, over 50% of HF patients develop resistance to loop diuretics. The molecular mechanisms underlying the development of diuretic resistance are not clear and may involve decreased NKCC2-mediated NaCl transport, enhanced distal tubule NaCl reabsorption, or decreased accessibility of the diuretic drug to the nephron lumen. Few studies have used the mouse as a model of cardiorenal syndrome after myocardial infarction (MI). We hypothesize that C57Bl6J mice would develop kidney damage several months after myocardial infarction (MI) and resistance to loop diuretics. Heart failure was induced in C57Bl6J mice through ligation of the left anterior descending coronary artery (LAD) and classified as MI group and compared to a sham surgery group (without ligation) as controls. Both groups were assessed for heart function by echocardiography and renal filtration function by measuring GFR (FITC inulin) in conscious mice. The response to diuretics was studied in metabolic cages, 7-8 months after MI. MI mice had a 50% reduction in ejection fraction (EF) 4 weeks after MI compared to sham group (MI: 29.94 ± 1.94, Sham: 67.02 ± 1.14, n= 8 each group, p<0.05). Decreased EF continued to be lower 6 and 12 months after MI. Six months after surgery, the MI group showed decreased GFR compared to Sham (MI: 0.50 ± 0.06, Sham: 0.75±0.05 μl/min, n= 5 MI, n=7 sham, p<0.05). Despite lower GFR, 24h-urinary albumin excretion was similar in both groups (n=8 each group). In metabolic cage studies, a saturating dose of the NKCC2 inhibitor bumetanide (20 mg/Kg), induced diuresis and natriuresis in sham mice (Delta UV: 1.96 ± 0.27 ml/4h, Delta UNa: 117.2 ± 11.02μmols/4h, UCl: 175.65 ± 13.01 μmols/4h, n= 6) but had a smaller effect in MI mice which exhibited an attenuated diuretic response (Delta UV: 0.88 ± 0.23 ml/4h, Delta UNa: 65.00 ± 4.53 μmols/4h, UCl: 102.89 ± 14.08 μmols/4h, n= 4, p<0.05 vs sham), indicative of loop diuretic resistance. To study if bumetanide resistance is secondary to enhanced distal convoluted tubule (DCT) NaCl reabsorption, we measured the diuretic response to the NCC inhibitor hydrochlorothiazide (HCTZ). HCTZ (100 mg/Kg) induced diuresis and natriuresis in sham mice (Delta UNa: 75.24±11.18μmols/4h, UCl: 39.44±10.15 μmols/4h, n= 10) and the diuretic response was slightly higher in the MI group (Delta UNa: 129.54±11.59μmols/4h, UCl: 94.61±11.56 μmols/4h, n= 12, p<0.05 vs sham). We conclude that chronic heart failure in C57Bl6J mice, decreases GFR and induces loop diuretic resistance. Loop diuretic resistance after MI may be secondary to enhanced DCT NaCl transport in mice. This model could be useful to study the mechanisms causing decreased renal function and loop diuretic resistance after MI and pursuing new therapeutic avenues. No funding was received by the authors for conducting this study. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.