Circannual leptin and ghrelin levels of the blue fox (Alopex lagopus) in reference to seasonal rhythms of body mass, adiposity, and food intake

Abstract

The aim of the study was to investigate the circannual rhythms of leptin and ghrelin in the blue fox, a variant of the endangered arctic fox, in relation to its seasonal cycles of body mass, adiposity and food intake. The effects of long-term fasting and exogenous melatonin treatment on these weight-regulatory hormones were also investigated. The leptin concentrations of the blue fox increased during the autumnal accumulation of fat and decreased during the wintertime and vernal weight loss periods. The leptin levels peaked 2-6 weeks before the maximum values were observed for the body mass indices, voluntary food intake, and body masses. The ghrelin concentrations fluctuated widely during the autumn but decreased in the winter in association with suppression of food intake. Exogenous melatonin advanced the seasonal changes in the food intake of the blue fox but did not affect the seasonal rhythms of leptin and ghrelin concentrations. The leptin concentrations did not respond to the 3-week fasting periods in a consistent way, but the ghrelin levels increased due to food deprivation. In addition to the amount of fat in the body the leptin secretion of the blue fox may be regulated also by other factors. The blue fox may also express seasonal changes in its leptin sensitivity. Our results reinforce the hypothesis that leptin does not function as an acute indicator of body adiposity in seasonal carnivores but rather as a long-term signal of nutritional status.

Photoperiod Influences the Central Effects of Ghrelin on Food Intake, GH and LH Secretion in Sheep

“…However, the raccoon dog, which displays autumnal fattening and winter sleep, has relatively low ghrelin concentrations in the winter compared with the summer when in captivity [42] but demonstrates no clear seasonal changes in circulating ghrelin concentrations in the wild [43]. In the arctic fox, which is an actively wintering carnivore, ghrelin levels fluctuate widely during the autumn, but decrease in the winter months in association with the suppression of food intake [44]. Overall, more research is needed to elucidate the role that ghrelin plays within seasonal appetite cycles in these species.…”

Physiological leptin resistance

“…Stężenie leptyny w osoczu u tego gatunku rosło jesienią, gdy zwierzęta intensywnie gromadziły tłuszcz, a następnie stopniowo ulegało obniżeniu zimą i wiosną wraz z obniżaniem masy ciała. Najwyższe stężenie tego hormonu obserwowano jednak na kilka tygodni przed osiągnięciem przez badane osobniki maksymalnej masy ciała (37).…”

“…U świstaka amerykańskiego obniżenie stężenia leptyny jest skorelowane w czasie z powiększeniem jąder, co przypada na późną jesień i wczesną zimę (8). Podobna zależność obserwowana jest u lisa polarnego, u którego masa i objętość jąder wzrasta od stycznia do lutego, osiągając maksimum w marcu, z początkiem sezonu rozrodczego (46); jednocześnie pod koniec zimy i wczesną wiosną obserwowane jest obniżenie stężenia leptyny w osoczu (37). W badaniach przeprowadzonych in vitro na szczurzych jądrach wykazano, że leptyna hamuje wydzielanie testosteronu (49), a u R. pumilio zaobserwowano ujemną korelację stężenia leptyny i testosteronu w osoczu (44).…”

Annual Changes in Serum Leptin Concentration in the Adult Female Japanese Black Bear (Ursus thibetanus japonicus)

“…After November 27, the bears entered hibernation and ate nothing during the hibernation period. It has been reported that no significant correlation is found between serum leptin concentrations and BMI or body mass in humans (obese patients) [1], raccoon dogs (Nyctereutes procyonoides) and blue foxes (Alopex lagopus) during fasting [19,21]. The serum leptin levels in these species may not be determined by only the amount of fat deposit in the body.…”