Doctoral Dissertations

Date of Award

8-1989

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Human Ecology

Major Professor

Roy E. Beauchene

Committee Members

Dileep S. Sachan, Betsy Haughton, Edward T. Howley

Abstract

The effects of calorie restriction and exercise on feed consumption, growth, and the pituitary-adrenal axis were studied in aging male Wistar rats. The study consisted of 4 experimental groups: Sedentary, ad libitum fed controls (A); Sedentary, diet restricted by feeding on alternate days (R); Exercised by swimming on alternate days, ad libitum fed (AE); Exercised by swimming on alternate days, diet restricted by feeding on alternate days (RE).

Training effect was verified by heart weight:body weight ratio. Exercise resulted in a significantly lower body weight, in spite of the fact that exercised animals ate more than the sedentary animals. Body weight curves of all the experimental groups were of similar shape, though R and RE were at a lower level than A and AE.

Pituitary-adrenal function was assessed by measuring serum ACTH and corticosterone concentrations, adrenal weight, hepatic glucocorticoid receptor concentration and hepatic tyrosine aminotransferase (TAT) activity. Serum ACTH and corticosterone concentrations increased significantly with age while TAT activity decreased and receptor concentration remained the same. Adrenal weights also increased with age, with the adrenal weights of AE increasing the most dramatically. In general, calorie restriction and exercise didn't have a major influence on the aging axis. An exception was observed in TAT activity, which decreased more gradually with age in calorie restricted rats.

Analyses for relationships between variables revealed a quadratic relationship between serum ACTH and corticosterone concentrations. Concentrations of both hormones rose as rats aged, though ACTH levels decreased early in life. Additionally, there tended to be an inverse relationship between TAT activity and corticosterone concentration.

In general, aging rats exhibited increased concentrations of ACTH and corticosterone and diminished TAT activity, while receptor concentration remained the same. These observations may be indicative of a loss of feedback loop integrity and possible changes at the cellular level such as in chromatin activity in relation to TAT synthesis. Neither calorie restriction or exercise were able to maintain the integrity of pituitary-adrenal function, though calorie restriction did preserve TAT activity to a small degree.

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