Seasonal reproductive endocrine profile of the raccoon dog (Nyctereutes procyonoides)—effects of melatonin and food deprivation

Abstract

The raccoon dog (Nyctereutes procyonoides, Canidae, Carnivora) is a middle-sized omnivore with excessive autumnal fattening and winter sleep. We studied adaptations of the species to boreal climate and photoperiod by following the plasma reproductive and thyroid hormone concentrations of farm-bred raccoon dogs (n=32) for 12 months. On August 16, 2000, and February 8, 2001, half of the raccoon dogs received continuous-release melatonin implants (the MEL group). The other half was sham-operated (the SHAM group). Between November 27, 2000, and January 25, 2001, half of the animals of both groups were fasted. The plasma testosterone concentrations of the MEL males peaked in February, a month earlier than in the SHAM males. Autumnal melatonin treatment also advanced the gestation period reflected by the plasma progesterone concentrations by seven weeks. Food deprivation in winter seems to accentuate the sex steroid response during the mating as the fasted males had higher testosterone concentrations than the fed males in February and March.

Continuous Melatonin Treatment and Fasting in the Raccoon Dog (Nyctereutes procyonoides) – Vernal Body Weight Regulation and Reproduction

“…During the later half of pregnancy in May, the concentrations declined simultaneously with the progesterone levels (Asikainen et al, 2003). There was a positive correlation between the leptin and progesterone concentrations of the SHAM females during their mating season and pregnancy, as observed previously during the human menstrual cycle (Hardie et al, 1997).…”

“…In female rodents, leptin accelerates the onset of puberty (Ahima et al, 1997;Chehab et al, 1997) but inhibits early follicular development (Kikuchi et al, 2001) and ovulation (Duggal et al, 2000). The male and female raccoon dogs experienced a rise in their leptin levels during the winter before the vernal part of the experiment started simultaneously with the increasing plasma testosterone and luteinizing hormone levels connected to the approaching mating season (Asikainen et al, 2003). These findings conform to the hypothesis of high leptin concentrations functioning as a permissive metabolic gate for mammalian reproduction.…”

“…Autumnal melatonin treatment advances the testicular recrudescence of male raccoon dogs and estrus of females (Xiao, 1996;Asikainen et al, 2003). In the same way, the autumn moult, the autumnal increase in the appetite and the changes in the concentrations of weight regulatory hormones are also advanced due to melatonin (Xiao, 1996;Nieminen et al, 2002;Asikainen et al, 2003).…”

“…In the same way, the autumn moult, the autumnal increase in the appetite and the changes in the concentrations of weight regulatory hormones are also advanced due to melatonin (Xiao, 1996;Nieminen et al, 2002;Asikainen et al, 2003). Vernal melatonin treatment, on the other hand, slows testicular regression, stimulates the growth of underfur and inhibits the growth of guard hairs (Xiao, 1996).…”

“…The MEL females had, however, higher leptin concentrations than the SHAM females on March 7 th , when the MEL females were pregnant. Thus their higher leptin concentrations may be considered as an indicator of the advancement of their mating season by the autumnal melatonin treatment (Asikainen et al, 2003). Exogenous melatonin has previously increased leptin concentrations in plasma of the mink (Mustela vison; Mustonen et al, 2000) and leptin gene expression in white and brown adipose tissues of the garden dormouse (Eliomys quercinus; Ambid et al, 1998).…”