[Slowing the progression of chronic renal insufficiency with captopril in rats with spontaneous arterial hypertension and adriamycin nephropathy].

INTRODUCTION

The role of hypertension in chronic renal failure (CRF) progression was described in 1914 by Volhard and Fahr [1], in 1940 by Rite and colleagues [2] and subsequently many studies described the effects of various antihypertensive drugs on regulation of blood pressure and CRF progression. The recent experimental and clinical studies especially emphasized the role of angiotensin converting enzyme (ACE) inhibitors in the regulation of hypertension and slowing down of CRF progression, but there are still issues for discussion and disagreement [2-14]. The aim of this study was to analyse the effects of captopril on clinical, biochemical and morphological changes in spontaneously hypertensive rats (SHR) with adriamycin (ADR) nephropathy.

SUBJECTS AND METHODS

Experimental animals. Adult (24 weeks) female spontaneously hypertensive rats (SHR), weighting about 200 g, were bred at the Institute of Medical Research, Belgrade. The rats were randomly divided in the following groups: 1.

CONTROL GROUP

12 SHR; 2. Adriamycin group (ADR): 27 SHR treated with adriamycin (2 mg/kg i.v. twice for 20 days); 3. Adriamycin-captopril group (ADR-C): 30 SHR treated with adriamycin and thereafter with captopril (60 mg/kg/day). Animals were followed-up for 18 weeks after second adriamycin injection. Systolic blood pressure was measured at 2 weeks intervals throughout the study. Blood and urine samples were collected in weeks--4, 6, 12, and 18. Morphologic studies. Rats were killed at weeks 6, 12 or 18 after the second adriamycin injection, when the kidneys were removed and fixed in neutral buffered formalin (10%). Paraffin embedded tissue sections 4 microns thick were stained with hematoxylin and eosin, periodic acid-Schiff reagent (PAS), Thrichrom Masson and Silver methanamin (Jones) for light microscopic study. A semiquantitative score was used to evaluate glomerular, vascular and tubulointerstitial changes. A minimum of 60 glomeruli for each kidney were examined, and the severity of the lesions was graduated according to the percentage of glomerular sclerosis from 0 to 10 (0--0%; 2--20%; 5--20-50%; 10--100%) [16]. Vascular changes were graduated from 0 to 3 according to hyalinosis in the walls of the artenoles (1--0%; 2--< 50%; 3--50-100%; 4--100%) [17]. Tubulointerstitial changes were semiquantitatively expressed by calculation of separately the index of interstitial fibrosis (0--0%; 2--< 20%; 5--> 20%; IQ--> 40%) and the index of interstitial infiltration and tubular atrophy (0--0%; 1--< 20%; 2--> 20%; 3--> 40% [18]. Results were presented as mean +/- SD. Differences between groups in functional data as well as morphologic lesions were studied by one-way analysis of variance and the unpaired T-test.

RESULTS

Captopril decreased systemic blood pressure in ADR SHR significantly, but failed to prevent proteinuria (Fig. 1). Urea and creatinine in serum progressively increased in all studied groups, but faster in ADR SHR groups than in controls (Table 1). Creatinine clearance decreased faster in ADR group than in ADR-C group, but without statistical significance (Table 1). Among sixty nine analysed rats at the beginning of the study, sixteen died during the study. The other animals (Table 1) were killed at weeks 6, 12 and 18; pathohistological changes of their kidneys with glomerular, vascular and tubulomterstial indexes are presented in Table 2. In control group of rats minimal glomerular and interstitial changes could be seen in week 18, mild tubular changes were present in weeks 12 and 18, and marked changes in blood vessels were manifested in week 12, as well as in week 18 (Fig. 2, Table 2), when their statistical significance was higher than in rats treated with adriamycin. Glomerular, tubular and interstitial changes were mostly pronounced in adriamycin treated rats and became more expressive during the experiment (Table 2, Fig. 3). In ADR-C group of rats captopril slowed down glomerular changes, but significantly in week 18 only (Table 2). The same was with interstitial changes (Table 2, Figs. 3-c, 4-c). Tubular and vascular changes were less in week 6 in ADR-C group than in ADR group, what was leveled off later in the study (weeks 12 and 18) (Table 2).

DISCUSSION

Although Richard Bright was probably the first person to notice that severe renal diseases were associated with changes of the cardiovascular system, Volhard and Farhr first described that high blood pressure was the major cause of progressive loss of renal function in chronic renal diseases [1]. Subsequently, many authors in their experimental and clinical studies described the effects of various antihypertensive drugs on regulation of blood pressure and slowing down of CRF progression. Various experimental models were used in their studies [8, 19-21]. With discovery of ACE inhibitors and first studies which pointed that this group of drugs effectively slowed down CRF progression, many authors studied their effects on systemic blood pressure regulation, reduction of glomerular hypertension and slowing down of CRF progression. Anderson, Rennke and Brenner studied the effects of "triple therapy" (reserpine, hydralazine and hydrochlorotiazide) and ACE inhibitor enalapril in rats with subtotal nephrectomy [3]. Enalapril decreased systemic blood pressure, glomerular hypertension, proteinuria and glomerular sclerosis [9, 22-24], while "triple therapy" reduced only systemic hypertension with no effect on glomerular hypertension and glomerular damage [25]. The same was described in uninephrectomised DOCA rats [26]. Raij and colleagues also described better effects of enalapril in relation to "triple therapy": enalapril reduced mesangial expansion and proteinuria [27]. Our study [8] as well as that of other authors [3, 25, 26] agree that ACE inhibitor captopril was better in comparison with hydralazine in slowing down glomerular sclerosis and mesangial expansion inspite of good regulation of blood pressure with both drugs. In ADR SHR, ACE inhibitors reduced proteinuria [6, 10, 20, 25], regulated systemic blood pressure (Fig. 1-a), decreased glomerular hypertension and glomerular sclerosis [7, 10, 25, 28, 29] which were also found in our experimental study (Fig. 1, Table 2). These were confirmed in clinical studies too: first, in patients with diabetic nephropathy [30] and later in patients with nondiabetic kidney diseases [6, 30-34]. In SHRs blood pressure increased from week 4 to 10, and after week 12 blood pressure was stabilized on a constantly higher level [36]. Our studied rats were 24 weeks old at the beginning of the study and they had stable hypertension in that period (Fig. 1-a). With the age in SHRs renal function aggravated very slowly, with little changes in glomeruli, higher in tubuloniterstitium [19] and the highest in blood vessels. SHRs developed glomerular changes very late inspite of hypertension, because glomeruli were protected with preglomerular vasoconstriction [37]. These mild changes described by various authors could be also seen in our study (Fig. 2, Table 2). Pathohistological changes in rat kidneys caused with anthracycline were first described by Stenberg and Phillips in 1967 [41]. Adriamycin (doxorubicin hydrochloride) induced syndrome nephroticum. Light microscopic study revealed no changes at the beginning of the study, but later (7-9 months) glomerular sclerosis, tubular dilatation and interstitial fibrosis developed which led to chronic renal failure [42, 43], (Fig. 3). Therapy with ACE inhibitor, captopril, in rats with adriamycin nephropathy lowered glomerular sclerosis [7, 12, 25, 28, 29], and mesangial expansion was very rare. In our earlier studies, captopril was found to decrease glomerular sclerosis in the early phase of adriamycin nephropathy in SHRs [8, 29], what was also confirmed in this study: captopril decreased glomerular and tubulointerstitial changes in weeks 6, 12 and 18 after second adriamycin injection, but had no effect on vascular changes (Fig. 4, Table 2). Favorable effects of captopril on tubulointerstiatial changes (especially interstitial) are very important because many authors have described recently better correlation between tubulointerstitial changes and CRF progression [17, 44-46], in comparison to glomerular changes and CRF. Besides, some authors have confirmed better effects of ACE inhibitors when they were given earlier before glomeruli were damaged [47].

CONCLUSION

In SHRs with ADR nephropathy treatment with captopril normalized systemic blood pressure, and slowed down CRF progression in their early stage. These functional changes correlate with significant slowing of glomerular and interstitial changes.