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


Ali Kiani 1 , *

1 Animal Sciences Group, Lorestan University, [email protected], IR Iran

How to Cite: Kiani A. Temporal Changes in Plasma Concentration of Leptin, IGF-1, Insulin and Metabolites Under Extended Fasting and Re-Feeding Conditions in Growing Lambs, Int J Endocrinol Metab. Online ahead of Print ; 11(1):34-40. doi: 10.5812/ijem.6529.


International Journal of Endocrinology and Metabolism: 11 (1); 34-40
Published Online: December 21, 2012
Article Type: Original Article
Received: May 26, 2012
Accepted: June 12, 2012


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-?-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-day-fasted 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.

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