Seasonal Weight Regulation of the Raccoon Dog (Nyctereutes procyonoides): Interactions between Melatonin, Leptin, Ghrelin, and Growth Hormone

Abstract

The raccoon dog (Nyctereutes procyonoides, Canidae, Carnivora) is a middle-sized omnivore with excessive autumnal fattening and winter sleep. We studied seasonal weight regulation of the species by following the plasma leptin, ghrelin, and growth hormone (GH) levels of farm-bred raccoon dogs (n = 32) for 6 months. In August, half of the raccoon dogs received continuous-release melatonin implants, and in November, half of the animals of both the sham-operated and melatonin-treated groups were fasted for 2 months. In the autumn, the plasma leptin and GH levels were low, but the ghrelin levels were relatively high and correlated positively with energy intake. This represents the period of energy storage. Leptin and GH levels peaked simultaneously in late October, and melatonin advanced the peaks by 1 week. Thereafter, the levels rapidly declined, representing the transition period from autumnal anabolism to wintertime catabolism. In the winter, the leptin and GH levels rose to high levels, but the ghrelin-leptin ratio was very low. This is the period of winter sleep, with fat accumulated in the autumn as the principal metabolic fuel. In the winter, leptin, ghrelin, and GH may work in synergy to increase lipolysis. GH may also induce winter sleep to the raccoon dog. Fasting had no effect on the hormone levels, unlike in humans and rodents. Instead of the amount of fat in the body, the main regulators of the levels of these hormones in the raccoon dog are presumably seasonal rhythms entrained by melatonin.

Effects of season, food deprivation and re-feeding on leptin, ghrelin and growth hormone in arctic foxes ( Alopex lagopus ) on Svalbard, Norway

“…The well-documented, seasonal fattening of wild arctic foxes on Svalbard, with the highest levels of body fat in November-December (20%) and the lowest in June-July (6%; Prestrud and Nilssen 1992), does not correlate with plasma leptin levels, either. This observation is similar to another canid, the raccoon dog, with plasma leptin levels decoupled from body adiposity during the winter with the highest seasonal leptin levels and falling body mass during winter sleep (Nieminen et al 2002).…”

“…Leptin protein could be measured in arctic fox plasma at concentrations comparable to leptin levels of other carnivores measured with the same method (Nieminen et al 2001(Nieminen et al , 2002Arnould et al 2002). Similar to the raccoon dog, plasma leptin concentrations were unaffected by fasting (Nieminen et al 2002), but increased during refeeding supporting the model of leptin being, at least at some points of the animalÕs seasonal cycles, an indicator of increasing adipose tissue mass. Further studies will be needed to ascertain whether the small number of cases could have masked a clearer correlation between body mass and plasma leptin levels.…”

“…5 Leptin-ghrelin ratios during food deprivation and refeeding in May (unfilled symbols) and November (filled symbols), in arctic foxes on Svalbard presented as the mean±SD increase in circulating leptin concentrations during the recovery period from food deprivation (Nieminen et al 2002) as the energy reserves (adipose tissue) are replenished. The results of the present study further enforce the hypothesis of leptin not always being an indicator of body adiposity in carnivores (Nieminen et al 2001(Nieminen et al , 2002Arnould et al 2002).…”

“…Food restriction and deprivation reduce circulating leptin levels in both normal and anorexic humans (Dubuc et al 1998;Eckert et al 1998), in mice (Ahima et al 1996) and bats (Myotis lucifugus;Widmaier et al 1997), while re-feeding increases them (Eckert et al 1998). In other species, however, this correlation is absent with no effects of long-term fasting on the plasma leptin levels of the raccoon dog (Nyctereutes procyonoides; Nieminen et al 2002) and an increase in circulating leptin concentrations during the first 24 h fasting in lactating Antarctic fur seals (Arctocephalus gazella; Arnould et al 2002).…”

“…In humans, plasma ghrelin levels decrease with obesity (Tscho¨p et al 2001), but increase in fasting rodents (Tscho¨p et al 2000). In the canid raccoon dog, however, plasma ghrelin levels are unaffected by 2 months fasting (Nieminen et al 2002). Exogenous melatonin decreases rat ghrelin levels (Mustonen et al 2001a) and has an advancing effect on the seasonal rhythms of raccoon dog leptin and GH levels (Nieminen et al 2002).…”