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

Abstract

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.