Activity of renal 11betahydroxysteroid dehydrogenase 2 (11betaHSD2) in stressed animals

The enzyme 11betaHSD2 protects the non-selective mineralocorticoid receptor from occupation by glucocorticoids in aldosterone target tissues. We studied the effect of stress elicited by intubation with a rubber catheter and administration of 10 ml of 0.45% NaCl (G3), of 10 ml of 200 mM HCl (G4) or intubation alone (G2) on the kinetics of the renal enzyme compared with untreated rats (G1). Microsomes were incubated with increasing masses of 3H corticosterone and 400 microM NAD at pH=7.4 during 5 minutes. Samples were extracted with ethyl acetate and analyzed by TLC. Results for n=4: Vmax for G1, 4.82 +/- 0.67. G2, 10.04 +/- 0.16***. G3, 9.16 +/- 0.74**. G4, 10.19 +/- 0.79*** pmoles/min/mg prot. Km for G1, 22.37 +/- 2.42. G2, 50.72 +/- 7.05*. G3, 55.25 +/- 8.37**. G4, 27.40 +/- 3.20 nM. (***p<0.001, **p<0.01 and *p<0.05 vs G1). All treatments increased Vmax. Intubation alone and gavage with 0.45% NaCl, but not with 200 mM HCl, increased Km. Taking together, the results could reflect a way to prevent occupation of type I receptors by increased levels of circulating glucocorticoids due to stressful situations. This protection seems more efficient under acidotic conditions causing--in addition to an increased Vmax--a low Km for the enzyme.