Lipid metabolism in the adipose tissues of a carnivore, the raccoon dog, during prolonged fasting.

Previous studies on laboratory rodents, rabbits, and humans have demonstrated that adipose tissue fatty acid (FA) mobilization is selective, and its efficiency is related to the molecular structure of FAs. This study was undertaken to find out whether such preferences of FA mobilization are a general feature of mammalian white adipose tissue (WAT) and are also manifested in carnivores. Fractional mobilization of a wide spectrum of FAs was studied by gas-liquid chromatography from six subcutaneous (scapular, rump, ventral) and intra-abdominal (omental, mesenteric, retroperitoneal) WAT depots of raccoon dogs (Nyctereutes procyonoides) fed or fasted for 2 months. Fasting stimulated the mobilization of shorter-chain saturated, mono-unsaturated (MUFAs), and polyunsaturated FAs (PUFAs). The effects of unsaturation and the position of the first double bond from the methyl end were more inconsistent. The effect of double-bond position may be due to chain shortening of longer-chain MUFAs and preferential utilization of n-3 PUFAs over n-6 PUFAs. Moreover, there were site-specific differences in fractional mobilization, the omental adipose tissue being the most divergent. The in vivo FA mobilization from the regional WAT depots of a carnivore was selective, and the molecular structure of the FA affected its efficiency.

Aviation noise does not impair the reproductive success of farmed blue foxes.

The aim of our study was to assess the effects of aviation noise on reproduction and cub mortality in farmed blue foxes. Eighty artificially inseminated blue fox vixens (45 primiparous and 35 multiparous) were exposed to aviation noise on 5 days when they were pregnant or had cubs. The noise during the exposures varied from 85 to 121 dB (L(AFmax)). Vixens (45 primiparous and 34 multiparous) on a farm without flight action acted as controls. Cubs were counted 1, 3, 7, 14 and 49 days postpartum and at the beginning of July. Litter size (cubs per whelped vixen), reproductive performance (cubs per mated vixen) and cub losses (lost cubs per whelped vixen) were analyzed from both experimental farms (A and C). The flight action had no effect on reproductive success. Reproductive performance in primiparous vixens was 4.2+/-3.8 and 4.3+/-3.6 cubs (ns, Mann-Whitney U-test) in the control and aviation group, respectively, while in multiparous vixens the corresponding figures were 7.1+/-4.4 and 7.3+/-3.8 cubs (ns). In general, litter size declined from birth to weaning (in primiparous vixens from 8.1+/-3.8 to 5.4+/-3.2 cubs, and in multiparous from 9.7+/-3.8 to 7.2+/-3.8 cubs, P<0.001, GLM for repeated measures). The decline was greater in primiparous than in multiparous vixens (P<0.01). There were no differences in total cub losses between the experimental groups (ns). Accordingly, the present results show that exposure to severe and repeated aviation noise does not impair the reproductive success of farmed blue foxes.

Selective fatty acid mobilization in the American mink (Mustela vison) during food deprivation.

The mobilization of fatty acids (FAs) during food deprivation is a selective process in laboratory rodents and humans. The site-specific differences in adipose tissue functions - e.g. energy storage versus insulation - should also affect the use of different FAs. To study this, 16 female minks were randomly assigned into the control group or fasted for 5 days. Preferential mobilization of n-3 polyunsaturated FAs (PUFAs) during fasting caused a decrease in the n-3/n-6 PUFA ratio in fat and liver. In addition, the minks utilized short-chain FAs efficiently in all fat depots, but long-chain FAs - 20:0, 20:1n-11, 20:1n-9, 22:1n-11 and 24:1n-9 - were preserved. The number of double bonds in the FA chain correlated positively with mobilization rate in the retroperitoneal fat. The observed negative correlation between mobilization rate and the location of the first double bond from the methyl end may be due to peroxisomal chain-shortening of long-chain FAs and not the double bond position per se. As a result, minks are able to preserve a low melting point and fluidity of the subcutaneous fat depots, which would be essential to a Northern semi-aquatic mammal.

Endocrine and metabolic alterations in the mink (Mustela vison) due to chronic phytoestrogen exposure.

Phytoestrogens are natural components of plant-based food items with beneficial health effects. The aim of the present study was to investigate the chronic effects of dietary phytoestrogens, genistein (8 mg kg(-1) day(-1)) and beta-sitosterol (50 mg kg(-1) day(-1)), on the weight regulation of the mink (Mustela vison). The parental generation was exposed from August 2002 to May-June 2003 to either beta-sitosterol or genistein, while the kits were exposed through gestation and lactation. Food consumption and body masses were monitored monthly. Plasma lipid, glucose, total protein and hormone (ghrelin, leptin, triiodothyronine and thyroxine) concentrations were measured from the parents in August 2002, January 2003 and at the end of the experiment in May-June 2003 when the kits were 21 days of age. Relative food intake was higher in the beta-sitosterol-exposed minks than in the control or genistein minks in September 2002. Plasma leptin and total protein concentrations were lower in the beta-sitosterol kits compared to the control kits. Furthermore, plasma ghrelin levels and liver phosphorylase activities of the mink kits were higher due to genistein exposure. In mink kits, exposure to both phytoestrogens reduced the plasma thyroxine concentrations. The kidney glycogen concentrations and the muscle phosphorylase activities of phytoestrogen-treated adult minks were elevated. The results of this study suggest that minks are sensitive to perinatal phytoestrogen exposure.

Hyperthermia and increased physical activity in the fasting American mink Mustela Vison.

The aim of this study was to investigate the thermoregulatory adaptations to fasting in a medium-sized mustelid with a high metabolic rate and energetic requirements. Sixteen farm-bred female American minks, Mustela vison, were divided into a fed control group and an experimental group fasted for 5 days. The deep body temperature (T(b)) of the minks was registered at 10 min intervals with intraabdominal thermosensitive loggers and the locomotor activity was videotaped continuously for 5 days during the fasting procedure. The T(b) of the fasted animals increased during the first day of fasting and decreased during the second day. After 3-4 days of fasting, the levels of physical activity and T(b) of the fasted minks increased above the levels of the fed animals. Significant increases in these parameters were observed at the beginning of the working day on the farm, during the feeding of the fed animals and around midnight. It is concluded that the mink differs from previously studied homeotherms in thermoregulatory and behavioral responses to fasting probably due to its high energy requirements and predatory success.

Physiological adaptations to fasting in an actively wintering canid, the Arctic blue fox (Alopex lagopus).

This study investigated the physiological adaptations to fasting using the farmed blue fox (Alopex lagopus) as a model for the endangered wild arctic fox. Sixteen blue foxes were fed throughout the winter and 32 blue foxes were fasted for 22 d in Nov-Dec 2002. Half of the fasted blue foxes were food-deprived again for 22 d in Jan-Feb 2003. The farmed blue fox lost weight at a slower rate (0.97-1.02% body mass d(-1)) than observed previously in the arctic fox, possibly due to its higher initial body fat content. The animals experienced occasional fasting-induced hypoglycaemia, but their locomotor activity was not affected. The plasma triacylglycerol and glycerol concentrations were elevated during phase II of fasting indicating stimulated lipolysis, probably induced by the high growth hormone concentrations. The total cholesterol, HDL- and LDL-cholesterol, urea, uric acid and total protein levels and the urea:creatinine ratio decreased during fasting. Although the plasma levels of some essential amino acids increased, the blue foxes did not enter phase III of starvation characterized by stimulated proteolysis during either of the 22-d fasting procedures. Instead of excessive protein catabolism, it is liver dysfunction, indicated by the increased plasma bilirubin levels and alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase activities, that may limit the duration of fasting in the species.

Endocrinologic adaptations to wintertime fasting in the male American mink (Mustela vison).

The aim of this study was to investigate the endocrine response to wintertime starvation in the male American mink (Mustela vison) fasted for 16 hrs, 2 days, 3 days, 5 days, or 7 days (n =10 per group). After 2 days of fasting, the plasma leptin concentrations decreased, along with the triiodothyronine, testosterone, and progesterone levels, and the blood monocyte counts. Leptin also seems to trigger the response to fasting in mustelids by inducing immunosuppression and downregulation of the reproductive and thyroid axes. The dramatic increase in the peptide YY concentrations after 3 days of fasting may be required to suppress gastrointestinal processes during food scarcity. The plasma insulin levels decreased, and those of glucagon increased after 5 days of fasting in association with efficient glucose sparing and lipid mobilization. Body energy stores cannot be wasted for growth during nutritional scarcity and, thus, the growth hormone levels of the minks decreased after 5 days of fasting. The plasma noradrenaline and cortisol concentrations also decreased after 3 and 7 days without food, respectively. The plasma ghrelin, adiponectin, resistin, thyroxine, adrenaline, or estradiol levels did not respond to fasting. The endocrine response to food deprivation is remarkably similar in divergent mammalian orders, indicating that the hormonal signals enhancing survival during nutritional scarcity must be evolutionarily old and well conserved.

Adaptations of the raccoon dog (Nyctereutes procyonoides) to wintering--effects of restricted feeding or periodic fasting on lipids, sex steroids and reproduction.

The raccoon dog (Nyctereutes procyonoides) is an omnivorous canid with autumnal hyperphagia and fattening followed by mid-winter passivity and fasting in boreal latitudes with seasonal snow cover. The effects of two different feeding levels (400 or 200 kcal/animal/d) or fasting (5-week fasting+1-week feeding+3-week fasting) on plasma lipids, sex steroids and reproductive success of farm-bred raccoon dogs (n=60 females and 24 males) were studied in winter. The body masses, body mass indices (BMIs) and levels of plasma triacylglycerols (TG), total cholesterol and low- and high-density lipoprotein cholesterol did not differ between the fed and the restrictively fed animals. During fasting, the plasma TG concentrations increased and the BMIs decreased, indicating the release of fatty acids from adipose tissue. After the fasting periods, the levels of plasma cholesterol and high-density lipoprotein cholesterol increased, whereas the TG levels decreased indicating the rebuilding of energy reserves. The fact that the different wintertime feeding regimes had no impact on the plasma glucose, total protein, cortisol, estradiol, progesterone or testosterone levels, or on the reproductive success, indicates versatile adaptive capacity in the species.

Thermoregulatory adaptations of the overwintering captive raccoon dog (Nyctereutes procyonoides) in boreal climate.

The raccoon dog (Nyctereutes procyonoides) is a nocturnal canid thought to utilise passive wintering strategy in the boreal climate. To record the deep body temperature (T(b)), 12 farmed raccoon dogs were implanted with intra-abdominal T(b) loggers on November 26, 2003. Between December 3, 2003 and January 27, 2004 half of the animals were fasted for 8 weeks. The amplitude of the diurnal T(b) oscillations increased due to fasting. However, the mean diurnal T(b) was lower in the fasted animals only during two occasions. Unlike observed previously in other species, not only did the raccoon dogs experience hypothermia between 0600 and 1000 hr but also hyperthermia between noon and 1800 hr. The fasted animals were as active as the fed animals measured after 42-43 days of fasting and there was a significant cross-correlation between physical activity and T(b). The nocturnal period of hypothermia is probably an adaptation to save energy during food deprivation. The diurnal hyperthermia could be explained by the opportunistic foraging behaviour of the species. Opposite to the established assumptions, the raccoon dog does not seem to enter winter sleep on fur farms. In the future it is important to determine if true winter sleep occurs in nature in the species.

Adaptations to fasting in the American mink (Mustela vison): nitrogen metabolism.

The aim of this study was to investigate the adaptations of protein metabolism to seasonal fasting in an actively wintering boreal carnivore. Fifty farm-bred male American minks Mustela vison were divided into a fed control group and four experimental groups fasted for 2, 3, 5 or 7 days. The responses of nitrogen metabolism to wintertime food deprivation were determined by measuring the rate of weight loss, the tissue total protein concentrations and the plasma amino acid, urea, ammonia, uric acid and total protein levels. The mink has relatively poor adaptations to food deprivation, as it is not able to prolong phase II of fasting with fat as the major metabolic fuel. Instead, the species has to derive a part of its energy requirements from the breakdown of body proteins. The end product of protein catabolism--urea--accumulates in its circulation, and the mink may not be able to recycle urea-N. Although the mink can still have a high body fat percent at the end of the 7-day fast, it appears to enter phase III of fasting with stimulated proteolysis during this period.

Adaptations to fasting in the American mink (Mustela vison): carbohydrate and lipid metabolism.

The aim of this study was to investigate whether the actively wintering American mink Mustela vison is strictly dependent on continuous food availability or if it has evolved physiological adaptations to tolerate nutritional scarcity. Fifty farm-bred male minks were divided into a fed control group and four experimental groups fasted for 2, 3, 5 or 7 days. The rate of weight loss was several-fold higher (1.5-3.2% day(-1)) in the mink than recorded previously in larger carnivores utilizing passive wintering strategies. The minks remained normoglycaemic, although their liver glycogen stores and glucose-6-phosphatase activities decreased during fasting. Adipose tissue constituted approximately 36% of their body mass after 7 days of food deprivation. Intra-abdominal fat, especially retroperitoneal but also mesenteric adipose tissue, were the most important fat depots to be hydrolyzed, but the ability of the mink to utilize its body lipids during fasting may be limited. The increased liver size, hepatic triacylglycerol accumulation and increases in the activities of plasma aminotransferases indicated liver dysfunction. Food deprivation also affected the red blood cell indices, and the blood monocyte and lymphocyte counts decreased suggesting immunosuppression during fasting. The results of the present study suggest that the mink has not evolved sophisticated adaptations to wintertime fasting.

Adiponectin and peptide YY in the fasting blue fox (Alopex lagopus).

Adiponectin (Acrp30) and peptide YY (PYY) are weight-regulatory hormones participating in the control of energy homeostasis. This study investigated the effects of long-term wintertime fasting on plasma Acrp30 and PYY levels in the carnivorous blue fox, a farm-bred variant of the arctic fox (Alopex lagopus). Plasma Acrp30 and PYY concentrations were determined with radioimmunoassays during a 22-day period of fasting, which led to a 20.3% reduction in body mass of the animals (n=32). Sixteen fed blue foxes served as the control group. Acrp30 and PYY were present in blue fox plasma at similar or lower levels as reported previously for other mammals. Fasting had no acute effects on Acrp30 or PYY concentrations of the blue foxes. However, the Acrp30 levels of the fasted blue foxes were 24%-48% higher than in the fed animals between days 8-22 of fasting. Fasted blue foxes also had 6.2-fold higher plasma PYY concentrations after 15 days of fasting. Acrp30 and PYY seem to play roles in the body weight-regulation of the blue fox during long-term fasting, but their specific functions and physiological significance remain to be determined.

Phytoestrogens alter the reproductive organ development in the mink (Mustela vison).

The aim of the present study was to examine the reproductive effects of two perorally applied phytoestrogens, genistein (8 mg/kg/day) and beta-sitosterol (50 mg/kg/day), on the mink (Mustela vison) at human dietary exposure levels. Parental generations were exposed over 9 months to these phytoestrogens and their offspring were exposed via gestation and lactation. Parents and their offspring were sampled 21 days after the birth of the kits. Sex hormone levels, sperm quality, organ weights, and development of the kits were examined. The exposed females were heavier than the control females at the 1st postnatal day (PND). The control kits were heavier than the exposed kits from the 1st to the 21st PND. Phytoestrogens did not affect the organ weights of the adult minks, but the relative testicular weight of the exposed kits was higher than in the control kits. The relative prostate weight was higher and the relative uterine weight lower in the beta-sitosterol-exposed kits than in the control kits. Moreover, the plasma dihydrotestosterone levels were lower in the genistein-exposed male kits compared to the control male kits. This study could not explain the mechanisms behind these alterations. The results indicate that perinatal phytoestrogen exposures cause alterations in the weight of the reproductive organs of the mink kits.

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

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.

Endocrine response to fasting in the overwintering captive raccoon dog (Nyctereutes procyonoides).

The raccoon dog (Nyctereutes procyonoides) is an omnivorous canid utilizing the passive wintering strategy in the boreal climate. Farmed raccoon dogs (n=12) were randomly assigned into two study groups on 26 November 2003. Between 3 December 2003 and 27 January 2004, half of the animals were fasted for 8 weeks and plasma weight-regulatory hormone concentrations determined on 26 November and 30 December 2003 and on 27 January 2004. The plasma peptide YY, ghrelin, and growth hormone (GH) concentrations increased due to food deprivation, while the T4 and Acrp30 concentrations decreased. Furthermore, the plasma GH concentrations were higher in the fasted raccoon dogs than in the fed animals, which had higher plasma insulin, glucagon, and T4 concentrations. However, fasting had no effect on the plasma leptin concentrations. The results confirm previous findings with unchanged leptin levels in fasting carnivores. Increased GH levels probably contribute to increased lipolysis and mobilization of fat stores. Ghrelin can also enhance lipolysis by increasing the GH levels. The decreased levels of T4 may reduce the metabolic rate. The plasma dopamine concentrations decreased due to fasting unlike observed previously in rats. Together with the unaffected adrenaline, noradrenaline, and cortisol concentrations, this suggests that food deprivation in winter does not cause stress to the raccoon dog but is an integral part of its natural life history.

Effects of fasting and exogenous melatonin on annual rhythms in the blue fox (Alopex lagopus).

The arctic fox (Alopex lagopus) is a winter-active inhabitant of the high arctic with extreme fluctuations in photoperiod and food availability. The blue fox is a semi-domesticated variant of the wild arctic fox reared for the fur industry. In this study, 48 blue foxes were followed for a year in order to determine the effects of exogenous melatonin and wintertime food deprivation on their reproductive and thyroid axes. Half of the animals were treated with continuous-release melatonin capsules in July 2002, and in November-January, the animals were divided into three groups and either fed continuously or fasted for one or two 22-day periods. Food deprivation decreased the plasma triiodothyronine and thyroxine concentrations probably in order to preserve energy due to a decreased metabolic rate. The same was observed in the plasma testosterone levels of the males but not in the plasma estradiol concentrations of the females. Exogenous melatonin advanced the autumn moult and seasonal changes in the voluntary food intake. It also advanced the onset of the testosterone peak in the males. The plasma estradiol levels of the females were unaffected, but the progesterone levels peaked more steeply in the sham-operated females. Melatonin exerted a strong influence not only on the reproductive axis of the males but also on the seasonal food intake. The species seemed quite resistant to periodic involuntary food deprivation.

Detection, analysis and interactions of plasma ghrelin, leptin and growth hormone in the mink (Mustela vison).

The aim of this study was to obtain basic knowledge of the plasma concentrations and interactions of weight regulatory hormones in juvenile minks (Mustela vison). Ghrelin, leptin, and growth hormone (GH) levels were validated and determined by radioimmunoassay methods from the plasma of 30 female and 30 male minks. The female minks had higher plasma ghrelin and GH levels than the males. The plasma ghrelin concentrations of the females correlated positively with their body masses (BMs). The plasma leptin levels did not differ between sexes, but there was a positive correlation between the plasma leptin concentrations and BMs in the male minks. When the data from the male and female minks were combined, the correlation between the leptin levels and the BMs was still clear, but this was not observed in the females alone. In the male minks, the plasma GH levels correlated positively with the BMs and with the plasma leptin concentrations. However, there was no correlation between the plasma ghrelin and GH or leptin concentrations. The hormone concentrations were quite similar to earlier measurements in other carnivores.