Effects of nitric oxide (NO) synthase inhibition on blood pressure and on the course of Heymann nephritis was examined in rats. L-N^G-nitroarginine-methylester (L-NAME, 10 mg/l00 ml in the drinking water for 12 weeks) was used as an inhibitor of NO synthase. Urinary excretion of guanosine 3’,5’-cyclic monophosphate (cGMP), a second messenger of NO, was used as an indirect estimate of NO activity. Rats were divided into the following groups: control, nephritis, L-NAME, and nephritis-L-NAME. Urinary cGMP excretion was lower in the nephritis group (p < 0.05) and in the nephritis-L-NAME group (p < 0.005) compared with controls. Plasma atrial natriuretic peptide (ANP) levels were elevated in the nephritis (p < 0.001) and in the nephritis-L-NAME groups (p < 0.05). L-NAME treatment alone did not have any effect on plasma ANP levels. Blood pressure rose progressively in all L-NAME-treated rats. Most marked albuminuria developed in the nephritis-L-NAME group. No differences in the immunohistological findings were observed between the nephritis and the nephritis-L-NAME groups. NO synthase inhibition causes hypertension and aggravates albuminuria in chronic nephritis. Moreover, nephritis itself may decrease the production of cGMP either as a consequence of blunted NO activity or, in addition, because of ANP resistance. It appears that NO synthase inhibition does not change the immunological course of Heymann nephritis but rather the increased hemodynamic load makes the course of nephritis worse.

Objective: To investigate effects of angiotensin I converting enzyme (ACE) inhibition in experimental nephritis during chronic inhibition of nitric oxide (NO) synthase. Methods: Rats with and without autoimmune Heymann nephritis were treated with a NO synthase inhibitor L-NAME (50 mg/100 ml) and/or an ACE inhibitor captopril (20 mg/100 ml) in drinking water for 12 weeks. Urinary cGMP excretion was used as an indirect measure of NO activity. Blood pressure, urinary albumin, nitrite and nitrate levels, plasma ANP, and plasma renin activity were measured. Kidneys were examined with light microscopy and immunohistochemical methods. Results: Captopril treatment protected rats receiving L-NAME and none of the captopril-treated rats died. Mortality was greatest in the nephritis-L-NAME (57%) and L-NAME (43%) groups. Captopril normalized cGMP excretion, blood pressure, and prevented partly the appearance of albuminuria. Peritubular infiltration of mononuclear cells was clearly enhanced in the nephritis-L-NAME group (found in 80% of the rats) as compared with the nephritis (20%), L-NAME (40%), and control (0%) groups. The peritubular cell infiltration caused by L-NAME was prevented by captopril treatment. L-NAME-induced hypertension was associated with cardiac hypertrophy and this was prevented by captopril. Conclusions: NO may play an important renoprotective role in disease progression of chronic membranous glomerulonephritis. Captopril prevents L-NAME-induced hypertension, improves survival, and ameliorates renal damage in this type of nephritis. Dysfunction of renal NO pathways may be an important factor causing progressive renal damage in chronic nephritis. Our results suggest that the dysfunctional renal NO system may be beneficially activated by ACE inhibitors.

Aims: We investigated angiotensin II and nitric oxide-cGMP pathway in the development of hypertension and renal damage in chronic experimental nephritis. Methods: Rats with autoimmune nephritis were treated for 12 weeks with AT1 receptor antagonist L-158,809 and/or ACE inhibitor captopril given in drinking water. Blood pressure, urinary albumin, and urinary excretion of cGMP were measured. Renal density of ACE, AT1 and AT2 receptors was determined by quantitative in vitro autoradiography. Results: L-158,809, captopril, and their combination decreased blood pressure and normalised urinary albumin excretion rate in rats with nephritis. In L-158,809-treated rats, cGMP excretion was increased compared to the vehicle-treated nephritic group suggesting that the dysfunctional nitric oxide system may be activated by angiotensin antagonism. In nephritic rats, AT1 and AT2 receptor binding densities in renal medulla were decreased, cortical AT receptor expression remained unchanged. Following L-158,809 treatment, both AT1 and AT2 receptor binding was suppressed. Conclusion: Long-term blockade of AT1 receptors in chronic nephritis has beneficial effects both on albuminuria and blood pressure being as effective as ACE inhibition or their combination. The stimulatory effect of AT1 receptor antagonism on cGMP production was not mediated by AT2 receptor-dependent mechanisms suggesting that AT1 receptor blockade per se favours activation of humoral pathways that stimulate cGMP production and potentially contribute to renal protection in chronic nephritis.

DOCA-NaCl treatment causes hypertension, accelerates development of proteinuria, and leads to glomerulosclerosis in rats with autoimmune Heymann nephritis. To study the mechanisms of kidney injury induced by renal haemodynamic load in chronic nephritis, we studied by immunohistochemistry the local expression of various cytokines, growth factors and adhesion molecules in the kidneys of Heymann nephritic rats with or without DOCA-NaCl-induced hypertension. The DOCA-NaCl-nephritis group developed hypertension and marked renal enlargement as compared with the nephritis group, the DOCA-NaCl group, and the controls. Albuminuria appeared earlier and was heavier in the DOCA-NaCl-nephritis group compared with the nephritic rats without DOCA-NaCl. Expression of IL-6, TNF-alpha, GM-CSF, b-FGF, NGF, TGF-beta, and ICAM-1 was enhanced in the kidneys of the DOCA-NaCl-nephritis group as compared with other groups, localized mainly in the glomerular mesangium (IL-6, GM-CSF, TGF-beta), glomerular and peritubular endothelium (ICAM-1), and collecting ducts (TNF-alpha, b-FGF, NGF, TGF-beta), possibly associated with the observed tubulointerstitial mononuclear cellular infiltration. Thus in autoimmune Heymann nephritis, DOCA-NaCl treatment causes hypertension and increased renal mass together with upregulation of local cytokine and growth factor production, which may further aggravate hypertension and accelerate progression of renal damage.