Altered regulation of renal sodium transporters in salt-sensitive hypertensive rats induced by uninephrectomy

Development of pharmacological screening method for evaluation of effect of drug on elevated pulse pressure and arterial stiffness

INTRODUCTION

Elevated pulse pressure (PP) and amplification of arterial stiffness (AS) are responsible for various cardiovascular disease and deaths. Numerous investigations have identified that different antihypertensive agents influence PP and AS differently. None of the previous studies described any reliable animal model particularly to screen drugs having effects on PP and AS. In present study, we developed an animal model to screen such drugs particularly affecting PP and AS.

METHODS

Elevation of PP and amplification of AS were induced in rats by uninephrectomy along with high salt intake (NaCl 4% w/v) for a period of six weeks, and weekly changes in body weight, PP, systolic, diastolic, mean pressure and pulse wave velocity (PWV) were estimated. After six weeks, collagen elastin ratio of aortic segment was estimated. Histomorphometry of abdominal aortic section of rats was done using trinocular microscope.

RESULTS

After six weeks, uninephrectomized rats that were kept on high salt drinking water shown significant increase (P < 0.001) in MAP, PP and PWV indicates that hypertension along with elevated PP developed in rats, and increase in collagen/elastin ratio (P < 0.001) as well as PWV as compared to normal rats indicates the increase in AS.

CONCLUSION

The development of condition of hypertension in conjunction with increase in PP and AS in rats can be used as in-vivo screening model to determine the potency of drugs for the treatment of hypertension or other cardiovascular diseases associated with high PP and AS.

Everything we always wanted to know about furosemide but were afraid to ask

Furosemide is a widely used, potent natriuretic drug, which inhibits the Na(+)-K(+)-2Cl(-) cotransporter (NKCC)-2 in the ascending limb of the loop of Henle applied to reduce extracellular fluid volume expansion in heart and kidney disease. Undesirable consequences of furosemide, such as worsening of kidney function and unpredictable effects on sodium balance, led to this critical evaluation of how inhibition of NKCC affects renal and cardiovascular physiology. This evaluation reveals important knowledge gaps, involving furosemide as a drug, the function of NKCC2 (and NKCC1), and renal and systemic indirect effects of NKCC inhibition. Regarding renal effects, renal blood flow and glomerular filtration rate could become compromised by activation of tubuloglomerular feedback or by renin release, particularly if renal function is already compromised. Modulation of the intrarenal renin angiotensin system, however, is ill-defined. Regarding systemic effects, vasodilation followed by nonspecific NKCC inhibition and changes in venous compliance are not well understood. Repetitive administration of furosemide induces short-term (braking phenomenon, acute diuretic resistance) and long-term (chronic diuretic resistance) adaptations, of which the mechanisms are not well known. Modulation of NKCC2 expression and activity in kidney and heart failure is ill-defined. Lastly, furosemide's effects on cutaneous sodium stores and on uric acid levels could be beneficial or detrimental. Concluding, a considerable knowledge gap is identified regarding a potent drug with a relatively specific renal target, NKCC2, and renal and systemic actions. Resolving these questions would increase the understanding of NKCCs and their actions and improve rational use of furosemide in pathophysiology of fluid volume expansion.

Long-term consequences of uninephrectomy in male and female rats

We investigated the effects of uninephrectomy (UNX) in 6-week-old male and female rats on blood pressure (BP), renal sodium handling, salt sensitivity, oxidative stress, and renal injury over 18 months postsurgery, studying control sham-operated and UNX-operated rats at 6, 12, and 18 months postsurgery, evaluating their renal sodium handling, BP, urinary isoprostanes, N-acetyl-β-D-glucosaminidase, and proteinuria before and after a 2-week high-salt intake period. At 18 months, plasma variables were measured and kidney samples were taken for the analysis of renal morphology and tissue variables. BP was increased at 6 months in male UNX rats versus controls and at 12 and 18 months in both male and female UNX rats and was increased in male versus female UNX groups at 18 months. UNX did not affect water and sodium excretion under basal conditions and after the different test in male and female rats at different ages. However, the renal function curve was shifted to the right in both male and female UNX rats. High-salt intake increased BP in both UNX groups at 6, 12, and 18 months and in the female control group at 18 months, and it increased proteinuria, N-acetyl-β-D-glucosaminidase, and isoprostanes in both UNX groups throughout the study. Renal lesions at 18 months were more severe in male versus female UNX rats. In summary, long-term UNX increased the BP, creatinine, proteinuria, pathological signs of renal injury, and salt sensitivity. Earlier BP elevation was observed and morphological lesions were more severe in male than in female UNX rats.