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Hourly measurement of plasma leptin and cortisol concentrations in non-pregnant ewes under group housing conditions over 23 hours

  • J. Dandrea (a1), S. Pearce (a1), G. Davidson (a2), C. Morrison (a3), P. Goddard (a2), D.H. Keisler (a3), T. Stephenson (a1) and M.E. Symonds (a1)...

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The closely related actions of cortisol and leptin (Ahima & Flier, 2000) are involved with appetite, tissue growth and maturation, energy balance and weight deposition so that resistance to either may lead to obesity. In normal weight humans, plasma leptin and cortisol exhibit diurnal variation, peaking during darkness and late afternoon (respectively). In sheep, the literature consensus is that plasma cortisol levels are greatest during daylight. Ovine plasma leptin is also reported to vary in response to photoperiod-driven changes (Bocquier et al., 1998) and such as alterations in voluntary feed intake as daylength changes. Daily circadian patterns, however, are thought to be entrained by the time of daily feed presentation (Marie et al., 2001). The aim of the present study was to investigate the diurnal variation in ovine plasma leptin in unrestrained animals with ad-lib access to hay and water in relation to their plasma cortisol profile over the same period. Remote blood sampling was employed in order to reduce sampling stress that would affect the animals’ plasma physiology.

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Ahima, R. S. & Flier, J. S. (2000). Leptin. Annual Reviews of Physiology 62: 413437.
Bocquier, F., Bonnet, M., Faulconnier, Y., Guerre-Millo, M., Martin, P. & Chilliard, Y. (1998). Effects of photoperiod and feeding level on perirenal adipose tissue metabolic activity and leptin synthesis in the ovariectomized ewe. Reproduction, Nutrition and Development 38: 489498.
Delavaud, C., Bocquier, F., Chilliard, Y., Keisler, D., Gertler, A. & G, K. (2000). Plasma leptin determination in ruminants: effect of nutritional status and body fatness on plasma leptin concentration assessed by a specific RIA in sheep. Journal of Endocrinology 165: 519526.
Goddard, P. J., Gaskin, G. J. & Macdonald, A. J. (1998). Automatic blood sampling equipment for use in studies of animal physiology. Animal Science 66: 769775.
Marie, M., Findlay, P. A., Thomas, L. & Adam, C. L. (2001). Daily patterns of plasma leptin in sheep: effects of photoperiod and food intake. Journal of Endocrinology 170: 277286.
JD was sponsored by a M.A.F.F. PhD studentship; SP was sponsored by a BBSRC PhD studentship. The project was sponsored by grants from The Society for Endocrinology and The University of Nottingham.

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