J. Codina, M. Vall and E. Herrera (1982). Comparative changes with age of the fasting response in circulating ketone bodies, glucose and insulin and oral glucose tolerance test in the rat. Comparative biochemistry and physiology. A, Comparative physiology, 71(2), 231-6. https://doi.org/10.1016/0300-9629(82)90393-0

PubMed 6121649

[Abstract]
1. Body weight loss in 48 hr fasted rats decreased with age. 2. Blood glucose and plasma RIA-insulin levels correlated negatively and positively respectively with body weight in fed rats. Fasting produced a greater fall in blood glucose and a smaller decrease in RIA-insulin in young than in old rats. 3. Blood ketone bodies correlated negatively with body weight after 48 hr fasting. 4. In oral glucose tolerance tests, blood glucose rose more in adult and old rats than in prepuberals when both fed and fasted. RIA-insulin levels rose more in prepuberals than in older rats when fed but not when fasted. 5. Changes in body composition and reduced insulin sensitivity with age are discussed.