NAD- and NADP-dependent 11 beta-hydroxysteroid dehydrogenase isoforms in guinea pig kidney with gossypol inhibition.
OBJECTIVE
To study the mechanism of gossypol-induced hypokalemia.


METHODS
The 11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) protein was prepared from guinea pig kidney. The activity of 11 beta-OHSD with NAD or NADP as the coenzyme was measured by HPLC in both control and gossypol treatment.


RESULTS
The Vmax and K(m) were 0.64 mmol.h-1/g protein and 0.07 mumol (cortisol) for NAD-dependent 11 beta-OHSD, 1.75 mmol.h-1/g protein and 0.21 mumol (cortisol) for NADP-dependent 11 beta-OHSD, respectively when 80 micrograms of enzyme protein was used. The inhibitory effects of gossypol on these two 11 beta-OHSD isoforms were different. The IC50 (95% confidence limits) were 50.2 (48.3-52.0) mumol of gossypol for NAD-dependent 11 beta-OHSD and 1143 (1098-1188) mumol of gossypol for NADP-dependent 11 beta-OHSD. The Ki was gossypol 96 mmol.L-1 for the former and 340 mmol.L-1 for the latter.


CONCLUSIONS
The NAD-dependent 11 beta-OHSD is a more critical physiologic mechanism than NADP-dependent 11 beta-OHSD for hypokalemia caused by gossypol.
D042842:11-beta-Hydroxysteroid Dehydrogenases; D000818:Animals; D003271:Contraceptive Agents, Female / Q000494:pharmacology*; D006072:Gossypol / Q000031:analogs & derivatives* / Q000494:pharmacology; D006168:Guinea Pigs; D006913:Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D007672:Kidney Cortex / Q000201:enzymology*; D008297:Male; D008861:Microsomes / Q000201:enzymology; D009243:NAD / Q000502:physiology; D009249:NADP / Q000502:physiology