Mineralocorticoid Receptor Activation by Aldosterone or Corticosterone Induces Hypertension, Myocardial Infarction and Proteinuria
Aldosterone through its interaction with the mineralocorticoid receptor (MR) plays a critical role in the development of hypertension and cardiovascular injury (CVI). Normally, MR is protected by 11β-hydroxysteroid dehydrogenase (11β-HSD) which inactivates glucocorticoids preventing their binding to MR. We hypothesis that if activation of MR by either aldosterone or glucocorticoids induces hypertension and CVI, then the inhibition of 11β-HSD with glycyrrhizin (GA), a natural inhibitor of 11β-HSD, should induce damage similar to that observed with aldosterone. Sprague-Dawley rats were uninephrectomized, and treated for 4 weeks with 1% NaCl (in drinking water) for the control group, 1% NaCl + aldosterone infusion (0.75 μg/h), or 1% NaCl + GA (3.5 g/l in drinking water). After 4 weeks, aldosterone and GA caused significant increases in blood pressure compared to control rats ([mean ± SEM] 211± 9, 205 ± 12, 120 ± 9 mmHg, respectively, p<0.001). Both aldosterone- and GA-treated rats had a significant increase in proteinuria (152.2 ± 8.7 and 107.7 ± 19.5 mg/d, respectively) versus controls (51.2 ± 9.5 mg/d). There was a significant increase (p<0.001) in heart to body weight ratio in the rats treated with aldosterone or GA compared with control (3.92 ± 0.10, 3.98 ± 0.88, and 3.24 ± 0.92 mg/g, respectively). Hearts of GA and aldosterone treated rats showed similar histological changes consisting of biventricular myocardial necrosis and fibrinoid necrosis of small coronary arteries and arterioles. These data suggests that in rodents activation of MR by either aldosterone or corticosterone leads to severe hypertension, vascular injury, proteinuria and myocardial infarction. Thus, 11β-HSD plays an important role in protecting the organism from injury.