Therapeutic resistance to angiotensin converting enzyme (ACE) inhibition is related to pharmacodynamic and -kinetic factors in 5/6 nephrectomized rats.

Proteinuria plays a pathogenic role in the development of end stage renal disease. Angiotensin converting enzyme (ACE) inhibitors lower proteinuria and are renoprotective. However, large inter-individual variation in antiproteinuric response to ACE inhibitors exists. In this study, we explored the mechanism of therapeutic resistance to an ACE inhibitor in the rat 5/6 nephrectomy model. At week 6 after 5/6 nephrectomy, treatment with lisinopril was initiated for 6 weeks. Proteinuria and blood pressure were evaluated weekly. At the end of the experiment, rats were divided into tertiles according to their antiproteinuric response: (1) responders (n=9), (2) intermediate responders (n=8) and (3) non-responders to ACE inhibitor therapy (n=9). At the start of treatment, proteinuria had progressively increased to 154 (95% confidence interval [CI]: 123-185) mg/24 h in the entire cohort, with comparable proteinuria and blood pressure in all groups. Following treatment with ACE inhibitor, proteinuria was significantly lower in the responders (68, CI: 46-89 mg/24 h) compared to the non-responders (251, CI: 83-420) mg/24 h). Similarly, blood pressure was reduced in the responders, but unaffected in the non-responders. At autopsy, renal ACE activity and renal ACE expression were significantly lower in the responders compared to the non-responders. Although lisinopril intake was comparable in all animals, urinary drug excretion was increased in the non-responders, demonstrating increased drug clearance. Average urinary lisinopril excretion was correlated with antiproteinuric response (R(2)=0.32, P=0.003). In conclusion, both pharmacodynamic and -kinetic factors account for the non-response to lisinopril. Whether these can be overcome simply by increasing drug dosage in non-responders should be investigated.

Altered myogenic constriction and endothelium-derived hyperpolarizing factor-mediated relaxation in small mesenteric arteries of hypertensive subtotally nephrectomized rats.

OBJECTIVES: Chronic renal failure (CRF) is associated with altered systemic arterial tone and hypertension. Myogenic constriction and endothelium-derived hyperpolarizing factor (EDHF)-dependent relaxation represent major vasoregulatory mechanisms in small systemic arteries. Elevated myogenic response and impaired EDHF might participate in the development of essential hypertension; however, their role in CRF-related hypertension is unknown. We investigated whether myogenic response and EDHF are altered in subtotally nephrectomized (sNX) rats and whether these changes are modifiable by chronic treatment with angiotensin-converting enzyme (ACE) inhibitor. METHODS: In a pressure arteriograph, myogenic constriction and EDHF-mediated relaxation were evaluated in small mesenteric arteries isolated from male Wistar rats 15 weeks after either sham operation (n = 7) (SHAM), sNX (n = 12) or sNX followed by 9 weeks of treatment with lisinopril (sNX + LIS, 2.5 mg/kg, n = 13). RESULTS: Surprisingly, myogenic response was reduced in hypertensive CRF rats (maximal myogenic tone: 37 +/- 2 and 18 +/- 4%, P < 0.01; peak myogenic index: -0.80 +/- 0.08 and -0.40 +/- 0.12%/mmHg, P < 0.05 in SHAM and sNX respectively). At the same time EDHF-mediated relaxation was also impaired (maximal response: 92 +/- 2 and 77 +/- 5%, P < 0.01; pD2: 6.5 +/- 0.1 and 5.9 +/- 0.1, P < 0.05). Both myogenic response and EDHF were inversely related to the severity of renal failure and restored by treatment with lisinopril to levels found in SHAM animals. CONCLUSION: Major constrictive (myogenic) and dilatory (EDHF) mechanisms of small systemic arteries are impaired in hypertensive CRF rats. These alterations do not seem to participate in the development of hypertension, being rather directly related to the severity of renal impairment. Both systemic vascular changes might be restored by renoprotective treatment with ACE inhibitor.

Renal targeting of captopril using captopril-lysozyme conjugate enhances its antiproteinuric effect in adriamycin-induced nephrosis.

INTRODUCTION: High-sodium intake blunts the renoprotective efficacy of angiotensin-converting enzyme (ACE) inhibitors. We investigated whether targeting the drug to the kidneys may attenuate the inferior response to ACE inhibitor (ACE-I) under high-sodium conditions. The ACE-I, captopril, was coupled to the low molecular weight protein (LMWP) lysozyme, yielding captopril-lysozyme conjugates that accumulate specifically in the proximal tubular cells of the kidneys. We compared the antiproteinuric efficacy of captopril to that of the captopril-lysozyme conjugate in adriamycin-induced proteinuric rats fed with a high-sodium diet. MATERIALS AND METHODS: Rats with adriamycin (single injection 2 mg/kg)- induced proteinuria were put on a high-sodium diet (HS; 3% NaCl). When stable proteinuria developed at 5.5 weeks, animals were assigned to the following subcutaneous treatments: (1) vehicle (n=7); (2) lysozyme (equivalent to the amount in conjugate) (n=7); (3) captopril (5 mg/kg/24 hours) (n=8); (4) captopril-lysozyme conjugate (captopril content equivalent to 1mg captopril/kg/24 hours) (n=7). Blood pressure and proteinuria were monitored. After 10 days of treatment the rats were sacrificed and kidneys and plasma were removed. RESULTS: Results are given as mean + S.E.M. After injection with adriamycin at t=0, stable proteinuria developed, amounting to 547+79 mg/24 hours at week 5.5. Subsequently, after seven and nine days of treatment, no reduction of proteinuria was observed in the captopril-treated group. In contrast, a significant reduction in proteinuria, amounting to 35+4% (day seven) and 25+2% (day nine), was observed in the captopril-lysozyme conjugate group (p<0.05 compared with the captopril group). In contrast, blood pressure was reduced in the captopril-treated group by 13.9+2.9 mmHg, while in the captopril-lysozyme treated group, an increase of 7.9+3.3 mmHg was found. Renal ACE activity was lowered by 30% in the captopril, as well as in the captopril-lysozyme conjugate treated group, compared with control. Furthermore, the ratio of kidney: plasma levels of captopril almost doubled as a consequence of coupling to lysozyme. CONCLUSION: In proteinuric rats fed with a high-sodium diet, captopril induced a reduction in blood pressure without an effect on proteinuria. In contrast, renal targeting of a five times lower dose of the ACE-I with the captopril-lysozyme conjugate reduced proteinuria without reducing blood pressure. Therefore, renal targeting of ACE-I may be a promising strategy to optimise the therapeutic response of ACE-I.

Endothelial function predicts the development of renal damage after combined nephrectomy and myocardial infarction.

It was demonstrated that individual renal endothelial dilatory function of the healthy rat predicts susceptibility to subsequent renal damage induced by 5/6 nephrectomy. In addition, it is reported that myocardial infarction (MI) that was performed upon unilateral nephrectomy (UNx) induced highly variable renal damage. Therefore, whether the variability in renal damage after MI could be explained by the variation in individual renal endothelial function before the induction of injury was studied. Endothelium-dependent relaxation to acetylcholine was investigated in vitro in small arteries that were isolated from the extirpated kidney at UNx. MI was induced 1 wk after UNx by ligation of the left coronary artery. Proteinuria and systolic BP were evaluated weekly for 16 wk thereafter using metabolic cages and the tail-cuff method, respectively. Upon termination of the study, focal glomerulosclerosis was evaluated by histology as an additional marker of renal damage. After MI, nephrectomized male Wistar rats (n = 15) gradually developed variable proteinuria, ranging from 20 to 507 mg/24 h at week 16, with an average systolic BP of 131 +/- 7 mmHg. The individual renal endothelial function of the healthy rats predicted the extent of renal damage in terms of proteinuria (r = -0.62, P = 0.008) and focal glomerulosclerosis (r = -0.70, P = 0.003). The individual level of renal endothelial function in the healthy rat is able to predict the severity of renal damage that is induced by MI. Further exploration of the underlying mechanisms may lead to discovery of preventive renoprotective therapies.