Inhibition of tissue repair by spironolactone: Role of mineralocorticoids in fibrous tissue formation

Mineralocorticoids have been implicated in promoting fibrous tissue formati on in various organs. In the present study, we sought to address the potent ial contribution of mineralocorticoids to fibrous tissue formation using a skin pouch model which has proved valuable for the analysis of inflammatory and wound healing responses. Skin pouches were induced in rats by administ ration of a phorbol ester, croton oil (0.5 ml of a 1% solution). After 2 we eks, rats were killed and intact pouch tissue collected. Pouch weights of c ontrol and aldosterone-treated (0.75 mu g/h via osmotic minipump) rats were similar (3.33 +/- 0.44 g vs. 3.70 +/- 0.28 g respectively). However, pouch weights were reduced by more than 50% in spironolactone-treated (25 mg/day powdered in food) animals (1.62 +/- 0.22 g and 1.27 +/- 0.23 g respectivel y in aldosterone and spironolactone alone groups). To ascertain the effects of different treatments on collagen accumulation, hydroxyproline concentra tion was measured. Compared with controls, hydroxyproline concentration was significantly reduced following spironolactone treatment (17.1 +/- 0.08 vs . 7.5 +/- 2.0 mu g/mg dry wt, respectively, p < 0.01). This response to spi ronolactone was negated by coadministration of aldosterone (hydroxyproline concentration was 18.6 +/- 2.1 mu g/mg dry wt). Following bilateral adrenal ectomy, spironolactone reduced pouch weight and hydroxyproline concentratio n, which was not the case for adrenalectomy alone. Two week aldosterone adm inistration in uninephrectomized rats on high salt diet was deemed ineffect ive in modulating pouch development (pouch wet wts were 3.48 +/- 0.4 g vs. 3.00 +/- 0.19 g in controls and aldosterone-treated rats, respectively). Mi neralocorticoid receptor expression in pouch tissue was demonstrated by RT/ PCR. Furthermore, NADP(+)-dependent 11 beta-hydroxysteroid dehydrogenase 1 (11 beta-HSD1) activity was detected in pouch tissue, together with lower l evels of NAD(+)-dependent 11 beta-HSD2. Spironolactone (p < 0.05) significa ntly reduced 11 beta-HSD1 activity compared with controls. Thus, fibrous ti ssue possesses requisite components of MC action, and antagonism of mineral ocorticoid receptors by spironolactone attenuates its formation. Pouch form ation is under the influence of circulating MC and, we would like to propos e, is also mediated through corticosteroids generated de novo at the site o f tissue repair.