Body fat content and feeding level interact strongly in the short- and medium-term regulation of plasma leptin during underfeeding and re-feeding in adult sheep.

Circulating leptin is regulated by food intake in the long, medium and short term; however, little is known about putative remnant effects of these successive regulations at any given time. To clarify this, two experiments were conducted in adult sheep, during which body condition parameters and plasma leptin were measured. During experiment 1, twenty ewes with normal body condition were either well fed (101 % of maintenance energy requirements (MER)) or underfed (41 % MER) for 166 d, then rapidly re-fed (at a mean of 208 % MER) for 3 d. Leptinaemia decreased after 14 d of underfeeding, remained depressed until day 166 and did not increase after 3 d re-feeding, whereas it was increased (+153 %; P < 0.05) by re-feeding the previously well-fed ewes. During experiment 2, twenty-four fat or lean ewes were either well fed (114 % MER) or underfed (52 % MER) for 94 d, and gradually re-fed for 2 d and maintained at a high feeding level (235 % MER) for 9 d. Underfeeding decreased leptinaemia in fat (from 4.19 to 2.63 ng/ml) but not lean ewes, and re-feeding increased leptinaemia after 5 d in lean previously well-fed (+123 %; P < 0.05) but not underfed ewes. In fat ewes, the impact of re-feeding was rapid (+144 %; P < 0.001 at 5 d) in previously well-fed ewes, whereas it was more gradual with a maximum at 11 d (+162 %; P < 0.01) in previously underfed ewes. In conclusion, leptinaemia is modulated by short-term energy intake level in interaction with long-term regulations involving nutritional history and body fatness, suggesting that a biological threshold of adiposity (about 20 %) is necessary to allow short- and medium-term leptin regulation.