Effects of age on control of lipolysis during fasting

Loss of body weight, girth, epididymal fat pad weight, and adipocyte size were examined in male, virgin, Wistar rats aged 2, 6, 12 and 22-24 months during 5 days of fasting. Relative reductions in all four parameters were greatest in the 2-month-old animals, with little differences among the older three age groups. In contrast, absolute weight loss was greatest in 12, and 24-month-old rats. Body weights were also greatest in these two groups. Plasma epinephrine and norepinephrine increased to the same levels in all 4 groups during the fast. Similarly, insulin decreased to the same levels in all groups although the oldest rats already exhibited low levels prior to fasting. Thus, possible age differences in the lipolytic response to fasting do not appear due to age-related differences in important lipolytic (catecholamine) and antilipolytic (insulin) hormone levels. Possible age-related differences in lipolytic response to fasting may instead reflect changes in other hormones which regulate lipolysis, or an altered sensitivity of adipocytes to such hormones.