HYPERADRENOCORTICISM AND FOOD RESTRICTION-INDUCED LIFE EXTENSION IN THE RAT - EVIDENCE FOR DIVERGENT REGULATION OF PITUITARY PROOPIOMELANOCORTIN RNA AND ADRENOCORTICOTROPIC HORMONE BIOSYNTHESIS

The increased diurnal elevation of plasma corticosterone (B) induced by food restriction (FR) may play a role in the life span extension of FR. We investigated whether FR alters adrenocorticotropic hormone (ACTH) and proopiomelanocortin (POMC) mRNA levels in plasma and anterior pituitary (AP), since these molecules both regulate and can be suppressed by B. Measurements were made in 3-month-old male Fischer 344 rats that had been fed ad libitum (AL) or FR (60% of AL calories) since 6 weeks of age. Plasma B was 2-fold higher in FR rats in the PM samples, but did not differ in AM samples. By contrast, plasma ACTH did not differ in the PM samples of FP and AL rats and was 20% lower in AM samples (p <.05) of FR rats. AP content of ACTH was 50% lower in FR rats in both AM and PM samples (p <.01). In contrast, AP contents of POMC mRNA, primary transcript, and processing intermediate were not reduced in FR rats, and PM content of POMC primary transcript was elevated in FR rats (p <.05). The reduced pituitary and plasma ACTH of FR rats may be the consequence of their elevated plasma B levels. This study also suggests that factors other than elevated ACTH account for FR-induced hyperadrenocorticism. These results also indicate that POMC mRNA and ACTH biosyntheses are differentially regulated in FR rats.