title: Food restriction enhances endogenous and corticotropin-induced plasma elevations of free but not total corticosterone throughout life in rats.
abstract: Chronic food restriction (FR), which retards many aging processes, enhances the endogenous diurnal peak of plasma total corticosterone (B) in young rats. Although the FR-dependent enhancement of total B disappears in aged rats, increased levels of the bioavailable fraction, free B, appear to be maintained. In young rats, we previously found that the FR-induced increase in the diurnal peak of total B is associated with increased adrenal response to corticotropin, also known as adrenocorticotropic hormone (ACTH). Here we show that the FR-enhanced adrenal response of total B to ACTH disappears with age but that the enhanced response of free B is maintained. We measured the endogenous diurnal peak and the response to ACTH of total and free B in 10-, 16-, and 22-month-old ad-libitum fed and FR male Fischer 344 rats in the afternoon, when plasma B peaks. At 10 and 16 months, FR rats showed enhanced total plasma B responses to ACTH relative to ad-libitum fed rats, but not at 22 months. By contrast, the response of free B to ACTH was enhanced by FR at all ages. The effect of FR on patterns of endogenous total and free diurnal B in these three age groups paralleled the ACTH-response data. The enhanced adrenocortical response of FR rats to ACTH does not reflect an increased expression of ACTH-receptor (ACTH-R) mRNA, because ACTH-R mRNA/microg adrenal RNA and ACTH-R mRNA/mg adrenal weight did not differ between ad-libitum fed and FR rats at any age.
authors.affiliation: Department of Physiology, The University of Texas Health Science Center, San Antonio, 78229-3900, USA. han@uthscsa.edu
authors.forename: E S
authors.initials: ES
authors.lastname: Han
authors.forename: T R
authors.initials: TR
authors.lastname: Evans
authors.forename: J H
authors.initials: JH
authors.lastname: Shu
authors.forename: S
authors.initials: S
authors.lastname: Lee
authors.forename: J F
authors.initials: JF
authors.lastname: Nelson
mesh_terms: D000311:Adrenal Glands / Q000033:anatomy & histology; D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000818:Animals; D003345:Corticosterone / Q000097:blood*; D002149:Energy Intake; D008297:Male; D009929:Organ Size; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011916:Rats, Inbred F344; D018043:Receptors, Corticotropin / Q000235:genetics
chemical_list: D012333:RNA, Messenger; D018043:Receptors, Corticotropin; D000324:Adrenocorticotropic Hormone; D003345:Corticosterone