title: Interpulse growth hormone secretion in the episodic plasma profile causes the sex reversal of cytochrome P450s in senescent male rats.
abstract: Humans as well as other mammals experience an aging-related decline in drug metabolism as well as a diminution in growth hormone secretion. In the case of rats, these events are more pronounced in senescent males, whose expression of male-specific isoforms of cytochrome P450, the major drug-metabolizing enzymes and constituting approximately 60-70% of the total cytochrome P450 in male rat liver, is completely suppressed, whereas female-dependent isoforms are remarkably induced to female-like levels. Overlooked in these independently reported studies is the fact that "signals" inherent in the masculine episodic and female continuous growth hormone profiles regulate expression and/or suppression of the dozen or so sex-dependent cytochrome P450 isoforms in rat liver. Whereas previous studies identified profound reductions in the pulse amplitudes of the masculine growth hormone profile as the cause for the diminished hormone secretion during aging, pulse heights are not recognized by the cytochromes as regulatory signals. Instead, we have shown that just a nominal secretion of growth hormone during the usual growth hormone-devoid interpulse period in the masculine episodic profile can explain the complete repression of male-specific CYP2C11, CYP3A2, and CYP2A2 and induction of female-dependent CYP2C12, CYP2C6, and CYP2A1 observed in senescent male rats.
authors.affiliation: Laboratories of Biochemistry, University of Pennsylvania School of Veterinary Medicine, 3800 Spruce Street, Philadelphia, PA 19104-6048, USA.
authors.forename: Ravindra N
authors.initials: RN
authors.lastname: Dhir
authors.forename: Bernard H
authors.initials: BH
authors.lastname: Shapiro
mesh_terms: D000375:Aging; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis; D015152:Blotting, Northern; D015153:Blotting, Western; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000737:chemistry; D000072467:Cytochrome P450 Family 2; D012734:Disorders of Sex Development; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins; D020033:Protein Isoforms; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D039181:Steroid 16-alpha-Hydroxylase / Q000096:biosynthesis; D013255:Steroid 21-Hydroxylase / Q000096:biosynthesis; D013250:Steroid Hydroxylases / Q000096:biosynthesis
chemical_list: D008565:Membrane Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; C400322:cytochrome P-450 CYP2C subfamily; D012313:RNA; D013006:Growth Hormone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; C089877:Cyp2c6v1 protein, rat; C465260:Cyp3a2 protein, rat; D051544:Cytochrome P-450 CYP3A; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; C029009:steroid hormone 7-alpha-hydroxylase; D013255:Steroid 21-Hydroxylase