FOOD RESTRICTION DIFFERENTIALLY AFFECTS MESSENGER-RNAS ENCODING THE MAJOR ANTERIOR-PITUITARY TROPIC HORMONES

Chronic food restriction (FR) leads to adaptive cellular changes, some of which retard aging. Moreover, some of these changes occur within w eeks after onset of FR. Because neuroendocrine mechanisms may mediate these effects, we measured the effect of FR on the messenger ribonucle icacids (mRNAs) encoding all of the tropic hormones of the anterior pi tuitary (AP). Slot blot and solution hybridization were conducted on A P ribonucleicacid (RNA) samples obtained at 0500 h (AM) and 1500 h (PM ) from 3-month-old male Fischer 344 rats fed ad libitum (AL) or FR (60 % of AL calories) since 6 weeks of age. PolyA RNA/mu g total RNA was s imilar in AL and FR rats, indicating that there was no overall effect of FR on mRNA levels. The level of proopiomelanocortin (POMC) mRNA was not reduced by FR when expressed per mu g of RNA or as total AP conte nt. By contrast, the total AP content of the mRNAs encoding LH beta, F SH beta, TSH beta, GH, and PRL was unmarkedly reduced by FR. When expr essed per mu g of RNA, however, only GH (AM and PM), FSH beta (AM), TS H beta (PM), and PRL (PM) were reduced by FR. These results reveal tha t FR differentially affects pituitary tropic hormone mRNA levels withi n weeks after onset of FR, and are consistent with a role for neuroend ocrine alterations in the initiation of adaptive cellular responses to FR.