Daily patterns of plasma leptin in sheep: effects of photoperiod and food intake

Abstract

Circulating concentrations of leptin in sheep correlate with body fatness and are affected by level of food intake and photoperiod. The present objective was to elucidate the short-term dynamics of leptin secretion. Frequent blood samples were taken over 48 h from 12 Soay rams after 16 weeks in short-day photoperiod (SD, 16 h darkness:8 h light) with freely available food, and then after 16 weeks in long days (16 h light:8 h darkness) with food freely available (LD) or restricted to 90% maintenance (LDR) (n=6/ group). During the second 24 h of sampling, half were food deprived (n=6, SD and LD) and half had their meal times shifted (n=6, SD and LDR). A homologous RIA was developed, using antibodies raised in chicken against recombinant ovine leptin, to measure plasma concentrations. Simultaneous 24 h profiles of plasma insulin, glucose and non-esterified fatty acids (NEFA) were measured. Plasma leptin was higher in LD than SD, and in LD than LDR, associated with higher food intake, liveweight and body condition score (adiposity), but tended to be lower in LDR than SD, associated with lower food intake, liveweight and body condition score. There was no evidence for a circadian rhythm of plasma leptin, but clear evidence for post-prandial peaks of low amplitude (15-36%) 2-8 h after meals given at normal and shifted times. Complete food deprivation caused a dramatic fall in plasma leptin to basal levels within 24 h. There was a positive association of plasma leptin with plasma insulin, and negative association with NEFA, both between meals and during fasting. Thus, plasma leptin concentrations in sheep are sensitive to short-term changes in energy balance, as well as to long-term photoperiod-driven changes in food intake and adiposity.

Follicle development, endocrine profiles and ovulation rate in adult Merino ewes: effects of early nutrition (pre- and post-natal) and supplementation with lupin grain

“…In this experiment, the 6-day lupin supplement increased the circulating concentrations of glucose, insulin, leptin and IGF1, as seen previously (Viñ oles et al 2005, 2010b, Scaramuzzi et al 2006. In this study, the changes associated with feed intake were evident for insulin, but not for glucose or leptin concentrations, in contrast to previous observations (Marie et al 2001, Viñoles et al 2005. The peak concentrations of glucose and the metabolic hormones occurred between days 2 and 5 after the start of feeding, a degree of variation that contrasts with the consistent increase on day 3 observed previously (Teleni et al 1989, Viñ oles et al 2005, and that appears to be explained by the level of pre-/post-natal nutrition.…”

Artificial long days in addition to exogenous melatonin and daily contact with bucks stimulate the ovarian and oestrous activity in Mediterranean goat females

“…The increase in LW in the LD-M group following the long-day treatment could be due to a direct effect of the long-day treatment, probably by increasing the food intake (Barenton et al, 1988). After, the LW decrease in the same group was probably due to the greater activity of animals as a consequence of the sexual activity induced (Walkden-Brown et al, 1997), and/or due to the decrease in food intake mediated by melatonin (Argo et al, 1999;Marie et al, 2001).…”

The effect of nutrition on the seasonality of reproduction in ewes

“…In sheep, malnutrition reduces gene expression and concentrations of circulating plasma leptin [52,53]. Furthermore, in sheep subjected to a longday photoperiod, leptin concentrations are higher [54,55], which probably reflects photoperiod-driven changes in intake and adiposity because food restrictions during long days reduce leptin concentrations to levels similar to those that occur during short-days [55].…”