Studies on the developmental and adrenal regulation of cytosolic and microsomal epoxide hydrolase activities in rat liver.
The present study was undertaken to ascertain developmental profiles of microsomal epoxide hydrolase (mEH) and cytosolic epoxide hydrolase (cEH) enzyme activities in rat liver. During development, mEH activity reached an optimum by 6 weeks of age (63 nmol/min/mg protein). Activities decreased thereafter in both sexes although in adult male liver the activity was twice that measured in adult female liver. Thus, the importance of pituitary maturation was suggested from these findings. Since glucocorticoids have been implicated in the regulation of mEH gene expression the effect of adrenalectomy on mEH activity was investigated in adult male rat liver. The procedure increased mEH activity almost two-fold and the increase was reversed by dexamethasone, but not deoxycorticosterone, administration. With respect to hepatic cEH activity, the developmental profiles indicated that enzyme activity was greatest in rats at 1 week of age (12-15 nmol/min/mg protein) and very little activity was detected beyond 4 weeks of age (approximately 5 nmol/min/mg protein); sex differences in cEH activity were not apparent at any age. Thus, the pituitary appears to be important in the developmental induction of mEH but not cEH. Glucocorticoids appear to provide the major hormonal influence on mEH expression. Thus, the hypothalamus-pituitary-adrenal axis is involved in the regulation of mEH but the regulation of the cEH enzyme remains unclear.
Horsfield
B P
BP
Department of Medicine, University of Sydney, Westmead Hospital, Australia.
Reidy
G F
GF
Murray
M
M
D000311:Adrenal Glands / Q000254:growth & development*; D000315:Adrenalectomy; D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D003600:Cytosol / Q000201:enzymology; D003900:Desoxycorticosterone / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004851:Epoxide Hydrolases / Q000378:metabolism*; D005260:Female; D008099:Liver / Q000201:enzymology* / Q000254:growth & development; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains
D003900:Desoxycorticosterone; D003907:Dexamethasone; D004851:Epoxide Hydrolases