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.     

Fertilization and early embryonic development in the blue fox (Alopex lagopus)

A total of 15 blue fox vixens aged 1–6 years were mated, 12 once on the first day of estrus and three a second time 48 hr after the first mating, and were killed 4 hr to 8 days following mating. Ova were collected from the oviducts, evaluated by stereomicroscopy, and studied by transmission (TEM; N = 49, 12 vixens) or scanning (SEM, N = 11, three vixens) electron microscopy. At 0–3 days after ovulation, the ova had not cleaved and were at different stages of meiotic maturation. In about one-half of these ova, representing all stages of meiotic maturation, a decondensing sperm head without nuclear envelope or a small pronucleus with partial nuclear envelope was observed. No clear relationship was found between maternal meiotic stage and the stage of paternal pronucleus formation. Sperm tails were never identified in the ooplasm. Cortical granules were released after sperm penetration at early stages of meiotic maturation. Thus the block against polyspermic penetration was activated during maturation of the oocyte. The first two-cell stage appeared 4 days after ovulation (3 days after mating), the first four-cell stage the following day (day 5), and the first eight-cell stage 6 days after ovulation (5 days after mating). In a single vixen mated late (7 days postovulation) two- to four-cell stages appeared the following day (day 8). This indicates that the time required for the first cleavage division decreases with increasing interval from ovulation to mating. The development of a functional nucleolus with fibrillar centers and fibrillar and granular components at the eight-cell stage indicates activation of embryonic RNA synthesis in fox embryos at the six- to eight-cell stage, suggesting that the embryonic genome is activated at this stage. © 1993 Wiley-Liss, Inc.     

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.     

Glucose turnover and defense of blood glucose levels in Arctic fox (Alopex lagopus)

1. Glucose utilization was assessed in fed and fasted arctic fox, maintained on a diet similar in composition to food available in the wild. 2. Fasted (24 hr) glucose concentration was not significantly different from the fed level (134 mg/dl). 3. Fasting was associated with a significant reduction in glucose space, pool size, total entry rate, and irreversible loss which suggests a decline in gluconeogenesis. 4. Glucose recycling was not significantly different between the fed and fasted states. 5. We suggest that, in the arctic fox, the mechanism for defending blood glucose levels during fasting is based on restricting blood glucose to tissues with a high glucose dependency.     

Milk intake in blue fox (Alopex lagopus) and silver fox (Vulpes vulpes) cubs in the early suckling period

Milk intake of fox cubs (2-16 days of age; body weight, 96-649 g) in ten blue fox litters and ten silver fox litters were measured by the water isotope dilution (WID) technique following a single intraperitoneal injection of tritiated water (3HHO). Litter size varied from four to 14 in blue foxes and from three to eight in silver foxes. Silver fox cubs had higher birth weights than blue foxes. Inter-species body weights and growth rates were apparently dependent on litter size and the dam's constitution. In both species growth rate increased with age and body weight (7-35 g per day). In the cubs, the biological half-life of body water turnover (BWT) rose from 1.5 days at 2-3 days of age to 2.5 days at 13-16 days of age, although a considerable scatter was seen. The mean daily milk intake of the cubs varied with body weight, from 31 to 193 g per day, whereas daily milk intake per unit of body mass remained stable at 30-35 g per 100 g body weight. The ratio of milk intake to body weight gain varied considerably among cubs, averaging 4.5 g/g during the 3-week experimental period. In suckling fox cubs, the calculated daily intake of metabolically energy (ME) corresponded fairly with the estimated energy requirements for growth and maintenance of the young. Finally, the applicability and the accuracy of the WID technique was evaluated in ten 3-week-old fox cubs, by tube-feeding with a milk replacer for 48 h, which documented that the daily rates of milk intake and water turnover can be accurately measured in suckling fox cubs by the WID technique following a single injection of 3HHO.     

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.     

Seasonal variations of plasma prolactin and LH concentrations in the female blue fox (Alopex lagopus)

A heterologous radioimmunoassay system developed for the rabbit and suitable for a wide range of mammalian species has been shown to measure prolactin in the plasma of the blue fox. Evaluation of prolactin levels throughout the year showed the concentrations displayed a circannual rhythm with the highest values occurring in May and June. Prolactin concentrations remained low (approximately 2.5 ng/ml plasma) from July until April with no consistent changes found around oestrus (March-April). In 8 pregnant females, the prolactin increase in late April and May coincided with the last part of gestation and lactation: concentrations (mean +/- s.e.m.) increased to 6.3 +/- 0.6 ng/ml at mid-gestation, 9.7 +/- 2.1 ng/ml at the end of gestation and 26.7 +/- 5.0 ng/ml during lactation. In 10 non-pregnant animals, the mean +/- s.e.m. values were 7.2 +/- 1.2 ng/ml in April, 8.8 +/- 2.2 ng/ml in May and 9.8 +/- 1.3 ng/ml in June. The prolactin profile in 4 ovariectomized females was similar to that observed in non-pregnant animals, but the plasma values tended to be lower during the reproductive season (April-June). In intact females, the only large LH peak (average 28 ng/ml) was observed around oestrus. During pro-oestrus, baseline LH levels were interrupted by elevations of 3.1-10.4 ng/ml. During the rest of the year, basal levels were less than 3 ng/ml. In ovariectomized females, LH concentrations increased within 2 days of ovariectomy and remained high (35-55 ng/ml) at all times of year.     

A variation of secondary sex ratio in blue fox (Alopex lagopus L.)

The effects of several genotypic and paratypic factors on the secondary (at birth) sex ratio was analyzed in blue fox bred in captivity. In particular, variation of sex ratio was for the first time studied as dependent on sire's age (without considering dam's age), the ages of both sire and dam, and the lines of both parents. The initial data were obtained from the Pushkino breeding facility, Moscow oblast. In total, 15,396 puppies were analyzed. The frequency of males (P) in this population was 0.551 +/- 0.004 (confidence interval 0.543 < p < 0.559). Parents' ages and litter size had no effect on the proportion of males in the progeny. In one of the two blue fox subpopulations under study, dam's line proved to be associated with a significant departure of sex ratio to a higher proportion of males, suggesting the effect of genotypic factors on the variation of secondary sex ratio in blue fox.     

蓝狐消化道内分泌细胞的免疫组化研究

蓝狐又名北极狐(Alopex lagopus),属于食肉目(Carnivora),犬科(Canidae),北极狐属(Alopex).     

Comparative nutrient digestibility of arctic foxes (Alopex lagopus) on Svalbard and farm-raised blue foxes (Alopex lagopus)

Arctic foxes from Svalbard (n=4) and farmed blue foxes (n=4) was used in a digestibility experiment with a high-carbohydrate feed to add more information to the nutritional physiology of the arctic fox, and to compare its digestive capacity with that of the farmed blue fox. The arctic fox has a diet containing mainly protein and fat from mammals and birds, while farmed blue foxes have been exposed to an omnivorous dietary regime for more than 80 generations. The experiment showed in general no difference in digestive capacity for protein and fat between the foxes (P>0.05), but for carbohydrates, including starch and glucose, the blue fox revealed higher digestibility values. The superior digestive capacity for carbohydrates in blue fox might be a result of a long-term selection of animals digesting dietary carbohydrates more efficiently, or that an early age exposition to dietary carbohydrates has given permanent improvement of the carbohydrate digestion in the gut.     

Study on the inheritance of the centric fusion in the blue fox,Alopex lagopus

The inheritance of a centric fusion in the blue fox,Alopex lagopus was investigated in 38 litters (258 animals) originated from matings of parents (64 animals) with all possible diploid numbers of chromosomes (2n=50, 49 and 48). In general, the Robertsonian translocation was inherited in accordance with the Mendelian principle. However, in the matings of females with 2n=49 and males with 2n=50 a significantly higher number of animals with 2n=50 was observed in the progeny. Moreover, observations on two litters indicated thede novo occurrence of the centric fusion and fission.     

Spermatozoon head size – the main differentiating feature between spermatozoa of blue and white Arctic fox (Vulpes lagopus)

Morphology and sperm morphometry, this is an important determinant of male reproductive capacity. Morphometric data may provide relevant information in studies focused on evolutionary biology, sperm quality assessment, including prediction of the potential fertility, semen cryopreservation, or the effect of reprotoxicants. The paper presents the morphometric analysis of spermatozoa from two colour morphs of Arctic fox (Vulpes lagopus), and attempts to determine the relationship between selected quality indicators and dimensions and shape of spermatozoa. The research material consisted of ejaculates collected once by manual stimulation from 20 one-year-old Arctic foxes (10 individuals of the blue morph and 10 of the white morph). Ejaculates were analysed for standard parameters (volume, sperm concentration, total number of spermatozoa in the ejaculate) and used for the preparation of microscopic specimens. It was found that, the dimensions of spermatozoa from Arctic foxes depend on the male colour morphs. Spermatozoa from white Arctic foxes were significantly longer (by 1.82 µm) and had larger heads (0.32 µm longer and 0.15 µm wider) compared to spermatozoa from blue Arctic foxes (P<0.05). The interactions between particular sperm dimensions indicated the occurrence of gametes differing in shape. The all correlation coefficients between the morphometric traits of spermatozoa were statistically significant. Our research proved that in the blue Arctic foxes, sperm dimensions (tail length and total sperm length) can be related to the percentage of spermatozoa with primary changes (respectively: r = -0.68 and r = -0.75; at P <0.05). However, in the case of white Arctic foxes, these characteristics depend on the ejaculate volume (respectively: r = 0.65 and r = 0.68; at P <0.05).     

Effect of melatonin implantation on the seasonal variation of FSH secretion in the male blue fox (Alopex lagopus)

A heterologous radioimmunoassay system developed for the sheep was shown to measure FSH in the plasma of the blue fox. FSH concentrations throughout the year showed a circannual rhythm with the highest values (61.6 +/- 14.8 ng/ml) occurring shortly before or at the onset of the mating season, a pattern similar to that of LH. The concentration of FSH then declined when androgen concentrations and testicular development were maximal at the time of the mating season (March to May). Thereafter, concentrations remained low (25.2 +/- 4.1 ng/ml) in contrast to those of LH. Implantation of melatonin in August and in February maintained high plasma values of FSH after the mating season (142.3 +/- 16.5 ng/ml) in association with a maintenance of testicular development and of the winter coat. The spring rise of prolactin was suppressed by melatonin treatment. The release of FSH after LHRH injection was also increased during this post-mating period in melatonin-treated animals, in contrast to the response of the control animals which remained low or undetectable. These results suggest that changes both in the secretions of FSH and prolactin may be involved in the prolongation of testicular activity and in the suppression of the spring moult after melatonin administration.     

The effect of sperm number on fertility in blue fox vixens (Alopex lagopus ) artificially inseminated with frozen silver fox (Vulpes vulpes ) semen

During the breeding seasons of 1989 and 1990, a total of 617 blue fox vixens aged 1 to 6 years (mean +/- SEM, 2.6 +/- 0.1) were inseminated with frozen silver fox semen with either 150 million (n = 213, 1989 + 1990), 100 million (n=172, 1990), 75 million (n = 119, 1989) or 37.5 million (n = 113, 1989) spermatozoa per insemination. Two intrauterine inseminations, each with an insemination volume of 1.0 ml, were performed at 24-hour intervals on the first and second days after maximum vaginal electrical resistance was measured. Conception rates were 87% (186 of 213) with 150 million spermatozoa per insemination, 85% (146 of 172) with 100 million, 77% (91 of 119) with 75 million and 68% (77 of 113) with 37.5 million. The mean numbers of cubs per litter +/- SEM for the four groups were 7.6 +/- 0.2 (168 registered litters), 7.5 +/- 0.3 (115 litters), 6.4 +/- 0.4 (86 litters) and 6.4 +/- 0.4 (75 litters). A negative effect on both the conception rate and mean litter size at whelping was observed with decreasing sperm numbers (conception rate percentage: p = 0.0001, Chi-square, litter size: p = 0.02, Kruskal-Wallis Test). Only the two larger numbers of spermatozoa gave litter sizes comparable to those obtained by artificial insemination (AI) with fresh semen.     

Photoperiod and fur lengths in the arctic fox (Alopex lagopus L.)

Pelage is seasonally dimorphic in the Arctic fox. During the winter, fur lengths for this species are nearly double similar values taken during the summer season. Considerable site-specific differences in fur length are noted. In general, body sites which are exposed to the environment when an Arctic fox lies in a curled position show greater fur lengths in all seasons and greater seasonal variations than body sites that are more protected during rest. Well-furred sites may tend to conserve heat during periods of inactivity, and scantily furred sites may tend to dissipate heat during periods of exercise. The growth of winter fur may compensate for the severe cold of the arctic winter. Changes in fur lengths indicate a definite pattern in spite of individual variations. During the fall months, fur lengths seem to lag behind an increasing body-to-ambient temperature gradient. Both body-to-ambient temperature gradients and fur lengths peak during December through February. From March through June, gradual environmental warming is accompanied by a decrease in average fur lengths. Thus, there appears to be a remarkable parallel between the body-to-ambient temperature gradient and the fur lengths. The growth of fur in the Arctic fox parallels annual changes in ambient temperature and photoperiod.Presented at the Eighth International Congres of Biometerorology, 9–14 September 1979, Shefayim, Israel.     

Seasonal variations of LH, prolactin, androstenedione, testosterone and testicular FSH binding in the male blue fox (Alopex lagopus)

The seasonal changes in testicular weight in the blue fox were associated with considerable variations in plasma concentrations of LH, prolactin, androstenedione and testosterone and in FSH-binding capacity of the testis. An increase in LH secretion and a 5-fold increase in FSH-binding capacity were observed during December and January, as testis weight increased rapidly. LH levels fell during March when testicular weight was maximal. Plasma androgen concentrations reached their peak values in the second half of March (androstenedione: 0.9 +/- 0.1 ng/ml: testosterone: 3.6 +/- 0.6 ng/ml). A small temporary increase in LH was seen in May and June after the breeding season as testicular weight declined rapidly before levels returned to the basal state (0.5-7 ng/ml) that lasted until December. There were clear seasonal variations in the androgenic response of the testis to LH challenge. Plasma prolactin concentrations (2-3 ng/ml) were basal from August until the end of March when levels rose steadily to reach peak values (up to 13 ng/ml) in May and June just before maximum daylength and temperature. The circannual variations in plasma prolactin after castration were indistinguishable from those in intact animals, but LH concentrations were higher than normal for at least 1 year after castration.