Renoprotective effects of chronic candesartan treatment in uninephrectomized rat

Candesartan prevents long-term impairment of renal function in response to neonatal partial unilateral ureteral obstruction

Angiotensin II (ANG II) plays an important role in the development of obstructive nephropathy. Here, we examined the effects of the ANG II receptor type 1 (AT1R) blockade using candesartan on long-term renal molecular and functional changes in response to partial unilateral ureteral obstruction (PUUO). Newborn rats were subjected to severe PUUO or sham operation (Sham) within the first 48 h of life. Candesartan was provided in the drinking water (10 mg·kg−1·day−1) from day 21 of life until 10 wk of age. Renal blood flow (RBF) was evaluated by MRI, glomerular filtration rate (GFR) was measured using the renal clearance of51Cr-EDTA, and the renal expression of Na-K-ATPase and the collecting duct water channel aquaporin-2 (AQP2) was examined by immunoblotting and immunocytochemistry. At 10 wk of age, PUUO significantly reduced RBF (0.8 ± 0.1 vs. 1.6 ± 0.1 ml·min−1·100 g body wt−1; P < 0.05) and GFR (37 ± 16 vs. 448 ± 111 μl·min−1·100 g body wt−1; P < 0.05) compared with Sham. Candesartan prevented the RBF reduction (PUUO+CAN: 1.6 ± 0.2 vs. PUUO: 0.8 ± 0.1 ml·min−1·100 g body wt−1; P < 0.05) and attenuated the GFR reduction (PUUO+CAN: 265 ± 68 vs. PUUO: 37 ± 16 μl·min−1·100 g body wt−1; P < 0.05). PUUO was also associated with a significant downregulation in the expression of Na-K-ATPase (75 ± 12 vs. 100 ± 5%, P < 0.05) and AQP2 (52 ± 15 vs. 100 ± 4%, P < 0.05), which were also prevented by candesartan (Na-K-ATPase: 103 ± 8 vs. 100 ± 5% and AQP2: 74 ± 13 vs. 100 ± 4%). These findings were confirmed by immunocytochemistry. Consistent with this, candesartan treatment partly prevented the reduction in solute free water reabsorption and attenuated fractional sodium excretion in rats with PUUO. In conclusion, candesartan prevents or attenuates the reduction in RBF, GFR and dysregulation of AQP2 and Na-K-ATPase in response to congenital PUUO in rats, suggesting that AT1R blockade may protect the neonatally obstructed kidney against development of obstructive nephropathy.

Effects of chronic chromium picolinate treatment in uninephrectomized rat

Chromium picolinate [Cr(pic)3] is a nutritional supplement that is advocated as an adjuvant therapy for impaired glucose tolerance/type 2 diabetes because it improves glucose homeostasis. Because renal dysfunction is a major complication of type 2 diabetes, the potential impact of Cr(pic)3 on kidney function requires due consideration. This investigation takes added importance because the kidney is not only the principal route of elimination for chromium but also an organ that preferentially accumulates it. To avoid the confounding influence of chronic hyperglycemia, and its associated complications, we used the unilaterally nephrectomized (UNX) rat that shows impaired kidney function with age. We tested the hypothesis that chronic treatment of the UNX rat with Cr(pic)3 exacerbates the age-related decline in renal function. Accordingly, UNX rats were fed a diet lacking (eg, control; n=5) or containing 5 mg/kg of Cr(pic)3 (n=7) for 60 days. The treatment did not affect glucose tolerance as reflected by lack of any effect on changes in blood glucose concentration during glucose tolerance testing. Although nonfasting blood glucose concentrations were similar between the 2 groups, plasma insulin concentration was lower in the Cr(pic)3-treated group (P<.05), suggesting improved insulin sensitivity. Body weight, blood pressure, heart rate, daily food and fluid consumption, daily urinary fluid and electrolyte excretions, urine osmolality, and daily protein excretion were similar between the 2 groups before and during Cr(pic)3 treatment. Although renal excretory responses to acute administration of a 5% isotonic saline volume load were similar between the 2 groups, the Cr(pic)3-treated group displayed a more robust ability to excrete a 10% isotonic saline volume load, an effect primarily related to reduced tubular reabsorption of the filtered fluid and sodium loads. In conclusion, chronic Cr(pic)3 did not adversely affect renal function. Rather, the treatment improved the ability of the animal to dispose of an acute isotonic saline volume load, suggesting preservation of renal function in the UNX rat.

Effect of hypertension and hypertension-glucose intolerance on myocardial ischemic injury

Systemic hypertension and type 2 diabetes mellitus are major risk factors for myocardial infarction. Yet, glucose intolerance, a prelude stage to type 2 diabetes, is associated with reduced infarct size. Since chronic hypertension adversely affects the myocardium, we tested the hypothesis that the coexistence of systemic hypertension and glucose intolerance reverses the cardioprotection associated with impaired glucose tolerance. Hearts from 9-month-old animals were subjected to a 40-minute occlusion of the left coronary artery followed by 2 hours of reperfusion. Before ischemia, similar values for the four experimental groups were observed for the coronary flow, heart rate, and maximum ventricular pressure. During the course of the ischemia-reperfusion insult, the two hypertensive groups displayed greater reductions in contractility than their normotensive counterparts. Infarct size was lower in the normotensive glucose-intolerant rat than in the normotensive control rat. Surprisingly, the hypertrophied hearts of the hypertensive and hypertensive glucose-intolerant rats displayed reduced infarct size (P<0.05). However, raising the afterload pressure from 100 to 160 cm H2O increased infarct size in the two hypertensive groups. This narrowed the differential between the hypertensive glucose-intolerant (160 cm H2O) and the normotensive control (100 cm H2O) rats. Nonetheless, at the higher afterload pressure, infarct size was less in the hypertensive glucose-intolerant rats than in their hypertensive counterparts. In conclusion, the impairment in contractile function despite the reduction in infarct size underscores the increased susceptibility of the hypertrophied, hypertensive heart to ischemic injury. Furthermore, exacerbation of cell death at elevated afterload pressure indicates the potential benefit of aggressive antihypertensive therapy.