Evidence for isoforms of 11 beta-hydroxysteroid dehydrogenase in the liver and kidney of the guinea pig.
In the human and in rodents like the rat and mouse, the liver enzyme 11 beta-hydroxysteroid dehydrogenase type I (11 beta-HSD-I) is a functional oxidoreductase preferring NADP+/NADPH as cosubstrate, while the renal isoenzyme (11 beta-HSD-II) prefers NAD+ as cosubstrate, and seems to be a pure oxidase and protects the tubular, mineralocorticoid (MC) receptor from occupancy by cortisol and corticosterone. We studied the enzyme kinetics of 11 beta-HSDs in kidney and liver microsomes of the guinea pig, a species whose zoological classification is still a matter of debate. With a fixed concentration of 10(-6) mol/l cortisol, liver and kidney microsomes preferred NAD+ to NADP+ (10(-3) mol/l) for the conversion to cortisone. Kidney microsomes converted cortisol to cortisone with K(m) values of 0.64 mumol/l and 9.8 mumol/l with NAD+ and NADP+ as cosubstrates respectively. The reduction of cortisone to cortisol was slow with kidney microsomes, but could be markedly enhanced by adding an NADH/NADPH regenerating system: with NADPH as preferred cosubstrate, the approximate K(m) was 7.2 mumol/l. This indicated the existence of both isoenzymes in the guinea pig kidney. Liver microsomes oxidized cortisol to cortisone with similar K(m) and Vmax values for NAD+ to NADP+ as cosubstrates (K(m) of 4.3 mumol/l and 5.0 mumol/l respectively). The NAD+ preference for the oxidation of 10(-6) mol/l cortisol described above may be due to a second, NAD(+)-preferring 11 beta-HSD with a K(m) of 1.4 mumol/l. In contrast to the kidney, liver microsomes actively converted cortisone to cortisol with a preference for NADPH (K(m): 1.2 mumol/l; Vmax: 467 nmol/min per mg protein). Thus, the main liver enzyme is similar to the oxidoreductase of other species (11 beta-HSD-I) and is also present in the kidney, while the main kidney enzyme is clearly NAD(+)-preferring. This kidney enzyme (analogous to 11 beta-HSD-II of other species) seems to be suitable for the protection of the MC receptor from the high free plasma cortisol levels of the guinea pig.
Quinkler
M
M
Division of Endocrinology, Klinikum Benjamin Franklin, Freie Universität Berlin, Germany.
Kosmale
B
B
Bähr
V
V
Oelkers
W
W
Diederich
S
S
D042842:11-beta-Hydroxysteroid Dehydrogenases; D000818:Animals; D003348:Cortisone / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D006854:Hydrocortisone / Q000378:metabolism; D006913:Hydroxysteroid Dehydrogenases / Q000032:analysis* / Q000378:metabolism; D007527:Isoenzymes / Q000032:analysis* / Q000378:metabolism; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D008862:Microsomes, Liver / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D018161:Receptors, Mineralocorticoid / Q000378:metabolism
D007527:Isoenzymes; D018161:Receptors, Mineralocorticoid; D009243:NAD; D009249:NADP; D006913:Hydroxysteroid Dehydrogenases; D042842:11-beta-Hydroxysteroid Dehydrogenases; D003348:Cortisone; D006854:Hydrocortisone