Assessment of effects in mink caused by consumption of carp collected from the Saginaw River, Michigan, USA

Polychlorinated hydrocarbons, including polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs), are ubiquitous environmental contaminants that bioconcentrate in the food chain. Numerous studies have demonstrated mink (Mustela vison) to be one of the most sensitive species to this group of compounds. In recent studies, a lesion characterized by osteoinvasion of epithelial cells into the mandible and maxilla of young mink fed diets containing 3,3',4,4',5-pentachlorobiphenyl (PCB 126) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was observed. The objective of the present study was to determine if proliferation of maxillary and mandibular squamous epithelia could be induced in ranch mink exposed to environmentally-derived polychlorinated hydrocarbons (PCBs, PCDDs, and PCDFs) in utero, during lactation, and throughout the growth period. Adult female mink were fed diets containing 0, 10, 20, or 30% carp (Cyprinus carpio) collected from the Saginaw River, Bay City, Michigan, USA, that provided 0.03, 0.83, 1.1, and 1.7 mg total PCBs (tPCBs)/kg feed and 2.5, 28, 47, and 73 ng TCDD toxic equivalents (TEQs)/kg feed, respectively, three weeks prior to breeding through weaning of the resulting offspring. Mink kits were maintained on their respective diets for up to 27 weeks of age. At 6 and 27 weeks of age, six to eight mink in each treatment group were necropsied and their jaws examined for evidence of maxillary and mandibular squamous epithelial proliferation. Results indicated that inclusion of up to 30% carp in the diet (1.7 mg tPCBs/kg feed, 73 ng TEQs/kg feed) had no effect on mink reproduction and kit survivability. However, maxillary and mandibular squamous epithelial proliferation was evident in four of the seven 27-week-old juveniles in the 20% carp group (1.1 mg tPCBs/kg feed, 47 ng TEQs/kg feed) and six of the eight juveniles in the 30% carp group (1.7 mg tPCBs/kg feed group, 73 ng TEQs/kg feed). Hepatic concentrations of tPCBs and TEQs increased in both the 6-week-old kits and the 27-week-old juveniles as the percentage of dietary carp increased. The livers of 6-week-old kits were also assessed for the presence of polybrominated diphenyl ethers, which increased as the percentage of Saginaw River carp in the diet increased.

Changes in thyroid and vitamin A status in mink fed polyhalogenated-aromatic-hydrocarbon-contaminated carp from the Saginaw River, Michigan, USA

A study was conducted to determine whether changes in thyroid and vitamin A dynamics were induced in ranch mink exposed to environmentally relevant concentrations of polyhalogenated aromatic hydrocarbons. Adult female mink were fed diets that contained 0% (control), 10%, 20%, or 30% wild carp (Cyprinus carpio) collected from the Saginaw River, Michigan, USA. Total polychlorinated biphenyls concentrations were 0.03, 0.83, 1.05, and 1.69 mg/kg feed, respectively; the 2,3,7,8-tetrachlorodibenzo-p-diozin toxic equivalents were 3.4, 27.9, 47.6, and 73.2 ng/kg, respectively. Diets were fed 3 weeks prior to breeding and throughout gestation and lactation. When the kits were weaned at 6 weeks of age, they were continued on their respective diets until 27 weeks of age. Plasma thyroid hormone concentrations, thyroid gland activity and structure, and vitamin A dynamics were assessed in young mink at 6 and 27 weeks of age. Plasma total T4 and free T4 in 6-week-old female and male kits fed the 10% carp diet were significantly higher than those of controls, while kits fed the 20% and 30% carp diet had nonsignificant decreases relative to the control mink. Plasma total T3 concentrations in 27-week-old juvenile males fed the 30% carp diet were significantly lower than those in individuals fed the 10% carp diet. No overt thyroid toxicity was apparent as thyroid weight, activity, and structure in kits and juveniles of both sexes were similar among diet groups. Plasma retinol and total ester concentrations in both kits and juveniles were reduced in mink fed the 30% carp diet relative to controls. The ratio of retinol to retinyl palmitate in livers of juveniles fed the 30% carp diet was two times higher than that in control mink. Significant reductions in kidney retinol and fatty acyl retinyl esters were observed in kits and juveniles fed the 30% carp diet relative to control values.

Temporal and spatial trends in chlorinated hydrocarbon concentrations of mink in Canadian Lakes Erie and St. Clair

Mink (Mustela vison) carcasses were collected from local commercial trappers from fall 1998 to spring 2003 from tributaries and marshes within 4.8 km from the shores of Lakes Erie and St. Clair, including the Wheatley Harbour and St. Clair River Areas of Concern (AOCs), as well as from inland sites (8 to 40 km from shore). Liver concentrations, on a lipid weight basis, of chlorinated hydrocarbons were measured and compared among sites and to tissue concentrations of mink from two previous collections from similar sites over the past 25 years. Mink from the western Lake Erie sites, which included the Wheatley Harbour AOC, had significantly higher concentrations of sum PCBs and PCB Aroclors than those from the St. Clair corridor or inland sites, with concentrations from the rest of Lake Erie being intermediate. Dieldrin concentrations were also significantly higher in western Lake Erie than many other sites, and those of oxychlordane and mirex also tended to be higher (0.05 < p < 0.1). There were no differences in contaminant concentrations between the St. Clair River AOC and the downstream non-AOC Lake St. Clair site, with the exception of slightly higher levels of octachlorostyrene (OCS). Concentrations of PCBs and other chlorinated hydrocarbons in mink showed a general decrease over the past two decades. In contrast, PCBs and some organochlorine pesticides tended to increase, significantly so with oxychlordane, in western Lake Erie mink over the same time period. DDE declined at all sites. Currently, mink liver PCB concentrations are within the range associated with reproductive impairment, as determined from captive mink studies, in 11.7% of all animals collected from the Lakes Erie and St. Clair basin overall, but in almost 40% of individuals from western Lake Erie.

Late development of homoeothermy in mink (Mustela vison) kits - a strategy for maximum survival rate*

The objective of this study was to establish the age at which mink kits develop functional homoeothermy. The investigation was based on the hypothesis that in this species with very immature neonates, late development of homoeothermy may be an adaptation to economize with energy. Measurements of heat production (HE) by means of indirect calorimetry lasting 3 h were performed on neonatal kits and kits from 1 to 54 days of age. Both single kits and groups of 4-5 huddling kits were kept at 15 degrees C (L) or 30 degrees C (H) [from 35 days onwards at 25 degrees C (H)]. Animals were weighed before and after the experiments and evaporative water losses (EWL) were calculated. When exposed to L temperature, single kits responded with a very low HE until 29 days of age, and groups of kits until 14 days of age. It was not until they reached an age of approximately 6 weeks that single kits showed a clear thermoregulatory response to the L temperature by increased HE, whereas groups of kits showed increased HE from 29th day onwards. When kept at H temperature, HE was low initially, but all kits showed elevated HE at 8 days of age, and the metabolic rate was similar for single kits and kits huddling in groups. Evaporative water losses was higher among single than among groups of kits and slightly lower but more variable for animals at L than at H temperature. It was concluded that mink kits develop functional homoeothermy at an age of close to 6 weeks and that the failure of very young kits to thermoregulate is an adaptation mechanism in order to economise with their very limited body energy reserves.

A first estimate of the amino acid requirement for milk production of the high-producing female mink (Mustela vison)

Thirty mink dams nursing litters of six kits were assigned to one of three dietary treatments [high protein (HP), medium protein (MP) and low protein (LP)], fed ad libitum for 4 week from parturition, to investigate the effects of protein supply on milk yield and milk composition in order to estimate the amino acid requirement of the lactating mink. Twelve dams were held in an intensive care unit and subjected to balance experiments and the kits were injected with deuterium oxide to determine water kinetics and milk yield. Eighteen dams were kept under normal farm conditions but with feed intake of dams and live weight gain of kits being determined and milk samples collected. The ME intake was higher (p < 0.05) in dams fed the LP and MP diets than in dams fed the HP diet, whereas the amino acid intake (g/day) was lowest (p < 0.05) in dams fed the LP diet. In the third and fourth weeks of lactation milk yield was higher (p < 0.05) in dams fed the LP and MP diets than in dams fed the HP diet. Chemical composition of milk was not affected (p > 0.05) by dietary treatment. However, protein content tended (p = 0.06) to be lower in dams fed the LP diet. Amino acid content (g/16 g N) of milk was higher (p < 0.05) in dams fed the LP and MP diets than in dams fed the HP diet. This resulted in the highest (p < 0.05) amino acid intake and highest (p < 0.001) live weights of kits nursed by dams fed the LP and MP diets, which may be explained by a combined effect of higher ME intake and reduced energetic costs for glucose production through less amino acids being used in gluconeogenesis. In conclusion, the improved performance of dams fed the LP diet suggested that their requirement of essential amino acids and non-specific N were covered, and the requirement of digestible amino acids of lactating mink (kg(0.75)) was, thereby, estimated by use of a factorial approach including the amino acid excretion in milk of LP dams.

Cortisol increases the activities of intestinal apical membrane hydrolases and nutrient transporters before weaning in mink (Mustela vison)

Glucocorticoids from endogenous and exogenous sources accelerate maturation of brush-border membrane (BBM) hydrolases in omnivorous laboratory rodents and pigs. Less is known for carnivores, and whether the route of administration (oral or systemic) has an influence. The present study examined the influence of administering cortisol (hydrocortisone succinate, 5 mg/kg-day) to mink during postnatal week 4, just prior to weaning, on small intestine glucose and amino acid (aspartate, leucine, lysine, methionine, proline) absorption and on the activities of BBM disaccharidases and peptidases. Kits treated with cortisol were smaller (P<0.05), but had small intestines that were proportionally larger (P<0.05 for length and mass per kg body weight, but not for mucosal mass) than control kits with higher rates of absorption for most nutrients, except leucine, and increased activities of most BBM hydrolases, except lactase. As a consequence, cortisol increased hydrolytic and absorptive capacities of the entire small intestine, with the responses more pronounced when the cortisol was given orally. These findings indicate administration of cortisol stimulates growth of the developing mink small intestine, but does not accelerate the postnatal declines in nutrient transport, and may be a dam-to-kit signal that prepares suckling mink to digest and absorb the adult diet.

Effect of extrusion on trypsin inhibitor activity and nutrient digestibility of diets based on fish meal, soybean meal and white flakes

The effects of moist extrusion processing of diets containing fish meal (FM) and conventional defatted soybean meal (SBM) or untoasted defatted soybean meal (white flakes [WF]) on amino acid composition, trypsin inhibitor activity (TIA), and apparent total tract digestibility of nutrients were studied. Three diets with the nutritional characteristics of feeds for salmonid fish were formulated: one control based on FM as protein source and two others where 40% of total amino acids from FM were substituted by either SBM or WF. Each diet was fed to mink either as an unextruded mixture of the ingredients or as extruded pellets in order to determine the effect of extrusion processing. Extrusion did not change the amino acid composition of the diets significantly, but reduced the TIA of both diets containing soy products by approximately 76%. Intake of the unextruded WF diet was only one-third compared with the other diets. The dry matter concentration in faeces from mink fed diets containing soy products was significantly lower than in mink fed the FM diet. Digestibility of crude protein, all amino acids and fat was lower, but starch higher, in the unextruded WF diet than in the FM and SBM diets, whereas no significant differences were found among the extruded diets. Extrusion of the WF diet increased digestibility of protein and all amino acids. The greatest increase in digestibility after extrusion of the WF diet was observed for cysteine followed by tryptophan. Extrusion of the FM and SBM diets had no significant effect on amino acid digestibility. Digestibility of starch was, in general, increased by extrusion. It is concluded that the heat treatment involved in typical moist extrusion processing used for fish feed may be sufficient to inactivate most of the TIA in unheated soybean meal, and to increase digestibility of the protein in WF to approximately the same level as found for SBM and FM. Still, extrusion is a lenient process with minor effects on nutrient digestibility of diets containing fish meal or toasted soybean meal as major protein sources.

Utilization of milk amino acids for body gain in suckling mink (Mustela vison) kits

The efficiency of utilization of milk amino acids for body gain in suckling mink kits from small (n = 3), medium (n = 6) and large litters (n = 9) was investigated by using 36 mink dams and their litters for measurements during lactation weeks 1 through 4. Measurements on each dam and litter were performed once, hence three dams per litter size each week (n = 9). Individual milk intake of kits was determined, milk samples were collected and kits were killed for determination of amino acid composition. The most abundant amino acids in milk were glutamate, leucine and aspartate making up about 40% of total amino acids. Branched chained amino acids made up slightly more than 20% and sulphur containing amino acids less than 5% of total milk amino acids. In kit bodies the sum of glutamate, aspartate and leucine made up about 32% of amino acids, branched chain amino acids about 16% and sulphur containing amino acids about 4%. The amino acid composition of both milk and bodies changed as lactation progressed with decreasing proportions of essential amino acids. The ratio between body and milk amino acids was constantly over 1 only for lysine, suggesting that it was the most limiting amino acid in mink milk. Milk amino acids were efficiently utilized during week 1, ranging from 74.7% (lysine) to 42.1% (leucine), with an average for essential amino acids of 58.4%. Tendencies for improved utilization of lysine (74.7-78.2%), phenylalanine (61.0-70.0%), histidine (62.4-68.8%), arginine (61.3-70.4%) and all essential amino acids (58.4-60.2%) from week 1 to week 2 were recorded. During weeks 3 and 4, the efficiency declined, and for all essential amino acids the average utilization was 38.1% during week 4.

Effects of mercury on neurochemical receptor-binding characteristics in wild mink

Piscivorous wildlife, such as mink (Mustela vison), routinely are exposed to mercury (Hg) in their natural environment at levels that may cause adverse behavioral outcomes. The purpose of this study was to determine if a correlation exists between neurochemical receptors and concentrations of Hg in the brains of wild mink. Specifically, receptor-binding assays were conducted to characterize the muscarinic cholinergic (mACh) and dopaminergic-2 (D2) systems in brain tissues collected from mink trapped in the Yukon Territory, Ontario, and Nova Scotia (Canada), and values were correlated with total Hg and methyl Hg (MeHg) concentrations in the brains. A significant correlation was found between Hg (total Hg and MeHg) and mACh receptor density (r = 0.546; r = 0.596, respectively) or ligand affinity (r = 0.413; r = 0.474, respectively). A significant negative correlation was found between total Hg and D2 receptor density (r = -0.340) or ligand affinity (r = -0.346). These correlations suggest that environmentally relevant concentrations of Hg may alter neurochemical function in wild mink, and that neurochemical receptor-binding characteristics can be used as a novel biomarker to assess Hg's effects on wildlife. Given the importance of the muscarinic cholinergic and dopaminergic pathways in animal behavior, further studies are required to explore the physiological and ecological significance of these findings.

Perfluorinated compounds in aquatic organisms at various trophic levels in a Great Lakes food chain

Trophic transfer of perfluorooctanesulfonate (PFOS) and other related perfluorinated compounds was examined in a Great Lakes benthic foodweb including water-algae-zebra mussel-round goby-smallmouth bass. In addition, perfluorinated compounds were measured in livers and eggs of Chinook salmon and lake whitefish, in muscle tissue of carp, and in eggs of brown trout collected from Michigan. Similarly, green frog livers, snapping turtle plasma, mink livers, and bald eagle tissues were analyzed to determine concentrations in higher trophic-level organisms in the food chain. PFOS was the most widely detected compound in benthic organisms at various trophic levels. Concentrations of PFOS in benthic invertebrates such as amphipods and zebra mussels were approximately 1000-fold greater than those in surrounding water, which suggested a bioconcentration factor (BCF; concentration in biota/concentration in water) of 1000 in benthic invertebrates. Concentrations of PFOS in round gobies were two- to fourfold greater than those in their prey organisms such as zebra mussels and amphipods. Concentrations of PFOS in predatory fishes (Chinook salmon and lake whitefish) were 10 to 20-fold greater than those in their prey species. Concentrations of PFOS in mink and bald eagles were, on average, 5- to 10-fold greater than those in Chinook salmon, carp, or snapping turtles. Because of the accumulation of PFOS in liver and blood, the biomagnification factor (BMF) of perfluorinated compounds in higher trophic-level organisms such as salmonid fishes, mink, and eagles were based on the concentrations in livers or plasma. Overall, these results suggest a BCF of PFOS of approximately 1000 (whole-body based) in benthic invertebrates, and a BMF of 10 to 20 in mink or bald eagles, relative to their prey items. Eggs of fish contained notable concentrations of PFOS, suggesting oviparous transfer of this compound. PFOA was found in water, but its biomagnification potential was lower than that of PFOS.

Kinetics of Glycosaminoglycan Deposition in Splenic AA Amyloidosis Induced in Mink

The kinetics of splenic glycosaminoglycan (GAG) expression in mink has been investigated during the course of AA amyloid induction, i.e. at 3 to 6 weeks of lipopolysaccharide (LPS) treatment. Splenic amyloid was demonstrated by means of Congo red staining in five of 19 LPS-treated mink. Chondroitin/dermatan sulfate (CS/DS), as well as heparan sulfate proteoglycans (HSPG), was extracted from amyloid and control spleens. Independently of the presence of amyloid, the total amount of splenic GAGs increased with the duration of LPS treatment, and an HSPG population was found confined to the LPS-treated spleens. The differential expression of various PG and GAG epitopes in mink spleen was investigated with the help of immunohistochemistry. The amyloid deposits were shown to contain GAG chains of CS and HS, and the core proteins of DSPG decorin and the HSPGs perlecan and agrin. Decorin and perlecan were shown in normal spleens localized to the splenic ellipsoids, an early target for AA amyloid deposition. The constitutive expression of PGs at predilection sites for amyloid deposition and their increased expression in the tissues developing amyloidosis at these early stages show that PGs are available for the formation and deposition of AA amyloid.

Short-term fasting induces intra-hepatic lipid accumulation and decreases intestinal mass without reduced brush-border enzyme activity in mink (Mustela vison) small intestine

For many mammalian species short-term fasting is associated with intestinal atrophy and decreased digestive capacity. Under natural conditions, strictly carnivorous animals often experience prey scarcity during winter, and they may therefore be particularly well adapted to short-term food deprivation. To examine how the carnivorous gastrointestinal tract is affected by fasting, small-intestinal structure, brush-border enzyme activities and hepatic structure and function were examined in fed mink (controls) and mink that had been fasted for 1-10 days. During the first 1-2 days of fasting, intestinal mass decreased more rapidly than total body mass and villus heights were reduced 25-40%. In contrast, tissue-specific activity of the brush-border enzymes sucrase, maltase, lactase, aminopeptidase A and dipeptidylpeptidase IV increased 0.5- to 1.5-fold at this time, but returned to prefasting levels after 6 days of fasting. After 6-10 days of fasting there was a marked increase in the activity of hepatic enzymes and accumulation of intra-hepatic lipid vacuoles. Thus, mink may be a useful model for studying fasting-induced intestinal atrophy and adaptation as well as mechanisms involved in accumulation of intra-hepatic lipids following food deprivation in strictly carnivorous domestic mammals, such as cats and ferrets.

Chronic fuel oil toxicity in American mink (Mustela vison): systemic and hematological effects of ingestion of a low-concentration of bunker C fuel oil

Petroleum oil enters the coastal marine environment through various sources; marine mammals such as sea otters that inhabit this environment may be exposed to low concentrations of petroleum hydrocarbons through ingestion of contaminated prey. The inability to perform controlled studies in free-ranging animals hinders investigations of the effects of chronic petroleum oil exposure on sea otter morbidity and mortality, necessitating the development of a reliable laboratory model. We examined the effects of oral exposure to 500 ppm bunker C fuel oil over 113-118 days on American mink, a species phylogenetically related to the sea otter. Hematological parameters and organs were examined for fuel oil-associated changes. Hepatic cytochrome P4501A1 mRNA expression and fecal cortisol concentrations were also measured. Ingestion of fuel oil was associated with a decrease in erythrocyte count, hemoglobin concentration (Hgb), hematocrit (HCT), and an increase in mean corpuscular volume (MCV). Total leukocytes were elevated in the fuel oil group from increases in neutrophils, lymphocytes, and monocytes. Significant interactions between fuel oil and antigen challenge were found for erythrocyte parameters, monocyte and lymphocyte counts. Liver and adrenal weights were increased although mesenteric lymph node weights were decreased in the fuel oil group. Hepatic cytochrome P4501A1 mRNA was elevated in the fuel oil group. Fecal cortisol concentration did not vary between the two groups. Our findings show that fuel oil exposure alters circulating leukocyte numbers, erythrocyte homeostasis, hepatic metabolism and adrenal physiology and establish a framework to use mink as a model for sea otters in studying the systemic effects of marine contaminants.

Utilization of milk energy by suckling mink kits

A total of 36 mink dams and their litters of 3, 6 or 9 kits were used for determination of milk intake of the suckling young by means of deuterium dilution technique, and chemical composition of milk and of kit bodies. Measurements were performed during lactation weeks 1-4, each week with 3 dams with each litter size. Milk intake was determined over a 48 h measurement period, and by the end of this milk samples were collected and 2 kits (litters of 6 and 9) or 1 kit per litter (litters of 3) were killed for body chemical composition. Based on the results, different models were applied for calculation of the energetic efficiency of milk. Dam milk yield increased steadily from week 1 until week 3 but only slightly from week 3 to 4. The increase declined with increasing litter size, and for dams suckling 9 kits the increment from week 3 to week 4 was only 2 g. The dry matter content of milk increased significantly as lactation progressed, being reflected in crude protein increasing from 6.9% in lactation week 1 to 8.1% in week 4. Milk fat increased concomitantly from 5.6% to 8.0%. In kit bodies, crude protein content increased from 9.4% in week 1 to about 12% in weeks 3 and 4. Body fat content increased from week 1 (4.1%) to week 3 (8.4%) and then declined in week 4 (7.1%). Animals suckled in litters of 3 kits had the highest milk intake and live weight and kits suckled in litters of 9 had the lowest milk intake, live weight and daily gain. In terms of milk intake per g gain kits in litters of 6 were the most efficient, with 4.1 g milk per g body gain. The metabolizable energy requirement for maintenance (MEm) was estimated to 448 kJ/kg(0.75 and the efficiency of utilization of ME for body gain (kg) to 0.67, the estimates being higher (MEm) or in good agreement with previous findings (kg) in suckling mink kits.

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.

Nursing sickness in the mink--a metabolic mystery or a familiar foe?

Nursing sickness, the largest single cause of mortality in adult female mink (Mustela vison), is an example of a metabolic disorder, which develops when the demands for lactation require extensive mobilization of body energy reserves. The condition is characterized by progressive weight loss, emaciation, and dehydration with high concentrations of glucose and insulin in the blood. Morbidity due to nursing sickness can be as high as 15% with mortality around 8%, but the incidence is known to vary from year to year. Stress has been shown to trigger the onset of the disease and old females and females with large litters are most often affected. Increasing demand for gluconeogenesis from amino acids due to heavy milk production may be a predisposing factor. Glucose metabolism is inextricably linked to that of protein and fats. In obesity (or lipodystrophy), the ability of adipose tissue to buffer the daily influx of nutrients is overwhelmed (or absent), interfering with insulin-mediated glucose disposal and leading to insulin resistance. Polyunsaturated fatty acids of the n-3 family play an important role in modulating insulin signalling and glucose uptake by peripheral tissue. The increasing demand on these fatty acids for milk fat synthesis towards late lactation may result in deficiency in the lactating female, thus impairing glucose disposal. It is suggested that the underlying cause of mink nursing sickness is the development of acquired insulin resistance with 3 contributing key elements: obesity (or lipodystrophy), n-3 fatty acid deficiency, and high protein oxidation rate. It is recommended that mink breeder females be kept in moderate body condition during fall and winter to avoid fattening or emaciation. A dietary n-3 fatty acid supplement during the lactation period may be beneficial for improved glycemic control. Lowering of dietary protein reduces (oxidative) stress and improves water balance in the nursing females and may, therefore, prevent the development and help in the management of nursing sickness. It is also surmised that other, thus far unexplained, metabolic disorders seen in male and female mink may be related to acquired insulin resistance.

Relationship of the hormone-sensitive lipase-mediated modulation of cholesterol metabolism in individual compartments of the testis to serum pituitary hormone and testosterone concentrations in a seasonal breeder, the mink (Mustela vison)

The role of cholesterol differs in the two compartments of the testis. In the interstitial tissue, cholesterol is necessary for the synthesis of testosterone, whereas in the seminiferous tubules, membrane cholesterol content in developing germ cells will influence the gametes' fertility. Here we evaluate the hormone-sensitive lipase (HSL) modulation of the cholesterol metabolism in each compartment of the testis. Two HSL immunoreactive bands of 104- and 108-kDa were detected in Western blots performed with polyclonal anti-human HSL antibodies in the interstitial tissue (ITf)- and seminiferous tubule (STf)-enriched fractions generated from testes harvested at 30-day intervals during puberty and, in the adult mink, during the annual seasonal reproductive cycle. Epididymal spermatozoa expressed a 104-kDa HSL isoform, and HSL was active in these cells. Immunolabeling localized HSL to interstitial macrophages; Sertoli cells, where its distribution was stage specific; spermatids; and the equatorial segment of spermatozoa. Total HSL protein levels, specific enzymatic activity, and free cholesterol (FC):esterified cholesterol (EC) ratios varied concomitantly in STf and ITf and reached maximal values in the adult during the period of maximal spermatogenic activity. In STf, HSL-specific activity correlated with FC:EC ratios but not with triglyceride levels. In STf, high HSL-specific activity occurred concomitantly with high FSH serum levels. In ITf, HSL-specific activity was high during periods of low serum prolactin levels and high serum testosterone levels. The results suggest that 1) modulation of cholesterol metabolism in individual testicular compartments may be regulated by HSL isoforms expressed by distinct cells; 2) interstitial macrophages may be part of a system involved in the synthesis of steroid hormones and in the recycling of sterols in the interstitium, whereas in the tubules, recycling could be ensured by Sertoli cells; 3) there is distinctive substrate preference for testicular HSL; and 4) HSL may be the only cholesterol esterase in this location.

Importance of the kidneys in metabolism of vitamins A1 and A2 and their fatty acyl esters in mink feeding on fish-based diets and exposed to Aroclor 1242

Two-month-old female mink (Mustela vison) were fed diets based on freshwater smelt (Osmerus eperlanus), Baltic herring (Clupea harengus membras), or North-Atlantic herring (Clupea harengus harengus) for 21 weeks. Half of the smelt-fed mink were exposed to the commercial polychlorinated biphenyl (PCB) preparation Aroclor 1242 (1 mg/day) in the feed. Retinol (vitamin A(1)), 3,4-didehydroretinol (vitamin A(2)), their fatty acyl esters, and vitamin E were studied in the kidneys by reversed-phase high-performance liquid chromatography. Exposure to Aroclor 1242 resulted a significant decrease in the alcoholic and esterified vitamin A(2). Levels of the A(1) analogs did not change due to the PCBs and were the same in mink fed either smelt or Baltic herring. In mink fed very fatty Atlantic herring, the renal levels of vitamin A(1) and E were significantly lower than in the other mink and apparently consumed by lipid peroxidation. The vitamins were located mainly in the cortex, and the fatty acyl esters showed a fatty acid composition that differed from those in liver and plasma. In the kidneys of the smelt-fed mink (control or Aroclor-exposed) the ratio of vitamin A(2) to A(1) was much lower than the ratios in the liver or plasma, suggesting inefficient uptake of A(2) in the kidneys. In the PCB-exposed mink, in which vitamin losses are increased, tissue levels of vitamin A(2) may be more difficult to maintain than levels of vitamin A(1).

Validation of a cell culture bioassay for detection of petroleum exposure in mink (Mustela vison) as a model for detection in sea otters (Enhydra lutris)

OBJECTIVE

To validate a luciferase bioassay, which is based on a recombinant mouse hepatoma cell line, for the detection of exposure to petroleum in mustelid species.

ANIMALS

122 American mink (Mustela vison) and 15 sea otters (Enhydra lutris).

PROCEDURES

Mink were exposed to Bunker C fuel oil or Alaska North Slope crude oil externally as a single exposure or internally via low dose concentrations in their ration for 6 months. Serum samples were analyzed for cytochrome P450 1A1 induction by quantification of luciferase activity in the bioassay. Mink liver specimens were also evaluated for cytochrome P450 1A1 induction by quantification of ethoxyresorufin-o-deethylase activity. Serum collected from exposed and unexposed sea otters was also analyzed using the luciferase bioassay.

RESULTS

Serum samples from mink externally exposed to petroleum had significantly increased luciferase activities at 1 week after exposure. Serum samples taken at later time points or from mink exposed to either product in the ration did not cause significant luciferase induction. Samples from otters exposed to petroleum had significantly higher luciferase induction as compared with samples from otters not exposed to petroleum at 2 and 8 years after the spill. Cytochrome P450 1A1 activity in liver specimens collected from mink that were internally exposed through diet was significantly increased at the conclusion of our study.

CONCLUSION AND CLINICAL RELEVANCE

The luciferase bioassay is a sensitive and specific method for determining recent exposure to petroleum in mink. The lack of luciferase activity in serum samples collected from mink greater than 1 week after experimental exposure was likely attributable to lower overall petroleum exposure in our trial, compared with natural exposures.

[Isozyme patterns of lactate dehydrogenase from tissues of mink and arctic fox during postnatal development]

Isozymes of lactate dehydrogenase extracted from heart, kidney, and liver of mink (Mustela vison Briss.) and Arctic fox (Alopex lagopus L.) during postnatal development were separated by agarose gel electrophoresis. Tissue-specific isozyme pattern of lactate dehydrogenase can be revealed at the age of one month, while the definitive pattern is formed at the age of four months. The isozyme patterns of lactate dehydrogenase in the studied tissues of mink and Arctic fox share the properties specific for animal species of various ecogenesis.

Glucose metabolism and regulation in lactating mink (Mustela vison)--effects of low dietary protein supply

Eighteen lactating mink raising litters of 6 to 7 kits were fed ad libitum from parturition on diets with 32% of ME derived from protein and decreasing fat:carbohydrate ratios [high fat:low carbohydrate (HFLC): 67:1, medium fat:medium carbohydrate (MFMC): 52:16, low fat:high carbohydrate (LFHC): 37:31]. Four weeks post partum the dams were fitted with a jugular vein catheter, and the experiment started with a 3 hours fasting period, after which the dams were fed 210 kJ ME of the experimental diets. Blood samples were collected 10 and 5 min before feeding and 30, 60, 90, 120, 150 and 180 min postprandially. Two hours postprandially a single dose of 50 microCi U-14C-labelled glucose was administered to each dam and blood samples were collected 5, 10, 20, 30, 45 and 60 min after the tracer administration. Plasma concentrations of glucose and insulin 30 to 120 min postprandially were higher in dams fed the LFHC diet, than in dams fed the HFLC diet, values for dams fed the MFMC diet being intermediate. Plasma glucagon concentrations were not significantly affected by dietary treatment. The glucagon:insulin ratios decreased postprandially in all dams, the response being significant in dams fed the LFHC diet. Plasma concentrations of urea were not significantly affected by dietary treatment. Plasma FFA concentrations tended to increase postprandially in dams fed the HFLC diet. Glucose turnover rates were approximately 4.0% per min in all dams, irrespective of dietary treatment. However, the daily glucose flux was lower in dams fed the HFLC diet than in dams fed the LFHC diet, and tended to be lower than in dams fed the MFMC diet. In conclusion, a dietary protein supply of 32% of ME simultaneously with a carbohydrate supply of 16% or 31% of ME had no adverse effects on glucose homeostasis or glucose metabolism in lactating mink.

High versus low protein diets to mink--postprandial plasma urea and creatinine response, osmotic load and pattern of nitrogen and electrolyte excretion

Nitrogen balance, pattern of excretion of nitrogenous end-products, endogenous urinary N excretion, postprandial plasma urea and creatinine, osmotic load, urinary electrolyte excretion and water intake/output relationships were studied in 12 adult female mink fed a high protein diet (HP; n = 6) providing about 155 g protein/kg or a low protein diet (LP; n = 6) providing about 95 g protein/kg. Two balance periods of each 3 d were used and diets were fed raw or cooked. After the last balance period followed a 48 h fasting period. Postprandial plasma urea and creatinine were studied for 48 h following a test meal given after an overnight fast. Osmotic load was determined based on collection of non-acidified urine carried out during 48 h. Level of protein supply did not affect N balance, being close to zero, whereas slightly negative balances were achieved for fasting animals. Protein supply was clearly reflected in excretion of urinary urea and allantoin but not in creatinine and uric acid. Endogenous urinary N excretion was estimated by a second order regression equation giving an intercept of 280 mg/kg0.75. Post-prandial plasma urea concentrations were strongly influenced by protein supply, HP animals having substantially higher peaks than LP animals, but values returned to fasting values within 24 h after the test meal. Plasma creatinine followed a biphasic pattern with a peak about 2 h after feeding and a nadir approximately 6 h after feeding. Physical form of diet influenced postprandial urea, animals fed raw diets having a higher peak, but not creatinine. The HP diet provided almost the double osmotic load of the LP diet and a corresponding increase in urine volume. The resulting water balances were identical irrespective of diet, showing that water intake/output relationships are very accurately regulated.