Temporal Changes in Plasma Concentration of Leptin, IGF-1, Insulin and Metabolites Under Extended Fasting and Re-Feeding Conditions in Growing Lambs

Background: a fall in plasma concentration of energy status related hormones (leptin, insulin-like growth factor-1 (igf-1) and insulin) and body energy expenditure occurs in response to short term fasting. nevertheless, the relations of the fasting-induced changes in energy related hormones and metabolites with fasting energy expenditure (fee) under extended fasting condition have received little attention so far. objectives: it is not clear how energy status related hormones coordinate to cope with feed deprivation under extended fasting time conditions and how quickly these hormones re-bound to fed-state values in response to re-feeding. thus the objectives of this study were: 1) to determine the effects of extended fasting on plasma concentration of leptin, igf-1, insulin, glucose, nefa, 3-β-hydroxybutyrate (bohb) and urea; and 2) to study the relations of energy status related hormones with fee and substrate oxidations under extended fasting conditions. materials and methods: eighteen six-month-old growing lambs (9 females and 9 males) were fasted for three days. blood samples were taken one hour before (-1h) and 48 and 72 hours after fasting (48h and 72h) and two hours after re-feeding (+2h) from jugular vein. during the last 22 hours of fasting, gas exchange (co2 production and o2 consumption) were measured using an open-circuit indirect calorimeter. respiratory quotient (rq), fee and relative proportions of oxidized protein, fat and carbohydrate were calculated. results: plasma levels of leptin, insulin, igf-1 and glucose decreased but nefa and urea levels increased within 48h of fasting. concentration of insulin significantly increased with extended fasting while leptin and igf-1 levels remained constant. glucose was the only blood variable that showed a quick re-bound within two hours after re-feeding. leptin and igf-1 showed significant positive relations with glucose and bohb but negative relations with nefa and urea. carbohydrate, fat and proteins contributed to 17%, 61% and 22% of fee respectively in three-dayfasted lambs. fee was negatively correlated with insulin and nefa concentrations in plasma. conclusions: even though plasma levels of leptin and igf-1 decreased and remained constant under extended fasting, neither leptin nor igf1 re-bounded to fed-status values within two hours after re-feeding. under extended fasting condition, firstly an insulin resistance develops and secondly, a fall in fee through a switch from carbohydrate- to fat-based metabolism occurs and there is an evident negative correlation between fee and plasma concentration of nefa.