Animal physiology. Summer declines in activity and body temperature offer polar bears limited energy savings.

Polar bears (Ursus maritimus) summer on the sea ice or, where it melts, on shore. Although the physiology of "ice" bears in summer is unknown, "shore" bears purportedly minimize energy losses by entering a hibernation-like state when deprived of food. Such a strategy could partially compensate for the loss of on-ice foraging opportunities caused by climate change. However, here we report gradual, moderate declines in activity and body temperature of both shore and ice bears in summer, resembling energy expenditures typical of fasting, nonhibernating mammals. Also, we found that to avoid unsustainable heat loss while swimming, bears employed unusual heterothermy of the body core. Thus, although well adapted to seasonal ice melt, polar bears appear susceptible to deleterious declines in body condition during the lengthening period of summer food deprivation.

Effect of protein supplementation on expression and distribution of urea transporter-B in lambs fed low-quality forage.

Two experiments were conducted to determine the effects of ruminal protein degradability, supplementation frequency, and increasing dietary protein on the expression and distribution of urea transporter-B (UT-B) in lambs fed low-quality forage (mature crested wheatgrass hay; 4.2 to 4.7% CP). In Exp. 1, 15 Dorset wether lambs (initial BW=45.8+/-1.3 kg) were blocked by initial BW and assigned to 1 of 3 treatments within a randomized complete block design for 28 d, with supplements fed to achieve 7, 10, or 13% total dietary CP. In Exp. 2, 13 Dorset wether lambs (initial BW=34+/-4 kg) were used in a completely randomized design and given 1 of 4 isonitrogenous supplements: 1) ruminally degradable protein (RDP) fed daily (n=3), 2) RDP fed on alternate days (n=3), 3) ruminally undegradable protein (RUP) fed on alternate days (n=3), or 4) a 50:50 mixture of RDP and RUP fed on alternate days (n=4) for 18 d. Alternate-day treatments were fed at twice that of daily supplementation. On the last day of both experiments, lambs were killed and samples taken for Western blot analyses for UT-B. Immunoblotting using a rabbit polyclonal antibody to UT-B confirmed the presence of distinct 32-kDa (consistent with a nonglycosylated UT-B protein) and 47-kDa (probable N-glycosylated form of UT-B) protein bands in all 9 tissues analyzed. In both experiments, the liver, dorsal rumen, reticulum, and ventral rumen displayed strong bands at 32 kDa and lighter bands at 47 kDa, whereas the cecum, large colon, spiral colon, and parotid salivary gland displayed slight 32-kDa bands and stronger, more visible bands at 47 kDa. Both protein bands were apparent in the kidney at similar visual intensities in Exp. 1, whereas the relative intensities of the 2 UT-B bands in the kidney were variable, and appeared somewhat reciprocal among animals in Exp. 2. Although the abundance of the 47-kDa UT-B band in the ventral rumen was greater (P=0.03) in lambs fed RDP daily in Exp. 2, no other treatment differences (P >or= 0.15 to 0.99) in the abundance of the 32- or 47-kDa UT-B proteins within tissues were observed in either experiment. Although protein supplementation strategy had little effect on UT-B expression in tissues other than the ventral rumen, differences in the degree of glycosylation of UT-B across tissues may provide insight into its regulation.

Hibernating bears conserve muscle strength and maintain fatigue resistance.

Black bears spend several months each winter confined to a small space within their den without food or water. In nonhibernating mammals, these conditions typically result in severe muscle atrophy, causing a loss of strength and endurance. However, an initial study indicated that bears appeared to conserve strength while denning. We conducted an in vivo, nonsubjective measurement of strength, resistance to fatigue, and contractile properties on the tibialis anterior muscle of six hibernating bears during both early and late winter using a rigid leg brace and foot force plate. After 110 d of anorexia and confinement, skeletal muscle strength loss in hibernating bears was about one-half that in humans confined to bed rest. Bears lost 29% of muscle strength over 110 d of denning without food, while humans on a balanced diet but confined to bed for 90 d have been reported to lose 54% of their strength. Additionally, muscle contractile properties, including contraction time, half-relaxation time, half-maximum value time, peak rate of development and decay, time to peak force development, and time to peak force decay did not change, indicating that no small-scale alterations in whole-muscle function occurred over the winter. This study further supports our previous findings that black bears have a high resistance to atrophy despite being subjected to long-term anorexia and limited mobility.

Hibernating black bears (Ursus americanus) experience skeletal muscle protein balance during winter anorexia.

Black bears spend four to seven months every winter confined to their den and anorexic. Despite potential for skeletal muscle atrophy and protein loss, bears appear to retain muscle integrity throughout winter dormancy. Other authors have suggested that bears are capable of net protein anabolism during this time. The present study was performed to test this hypothesis by directly measuring skeletal muscle protein metabolism during the summer, as well as early and late hibernation periods. Muscle biopsies were taken from the vastus lateralis of six free-ranging bears in the summer, and from six others early in hibernation and again in late winter. Protein synthesis and breakdown were measured on biopsies using (14)C-phenylalanine as a tracer. Muscle protein, nitrogen, and nucleic acid content, as well as nitrogen stable isotope enrichment, were also measured. Protein synthesis was greater than breakdown in summer bears, suggesting that they accumulate muscle protein during periods of seasonal food availability. Protein synthesis and breakdown were both lower in winter compared to summer but were equal during both early and late denning, indicating that bears are in protein balance during hibernation. Protein and nitrogen content, nucleic acid, and stable isotope enrichment measurements of the biopsies support this conclusion.

The role of dietary fatty acids in the evolution of spontaneous and facultative hibernation patterns in prairie dogs.

The white-tailed prairie dog is a spontaneous hibernator which commences deep torpor bouts during early fall while the black-tailed prairie dog is a facultative hibernator that will only enter shallow torpor when stressed by cold and food deprivation. Plant oils rich in polyunsaturated fatty acids (PUFAs) enhance the duration and depth of mammalian torpor. Thus, we tested the hypothesis that black-tailed prairie dogs sampled in the field have less PUFAs in their diets and that the enhancement of torpor bouts by this species on a diet higher in PUFA is less profound than that by white-tailed prairie dogs. Individuals of both species fed a high PUFA diet: (1) entered torpor earlier, (2) had lower torpor body temperatures and (3) had longer bouts of torpor, compared to those on a low PUFA diet. However, the magnitude of this change was similar for both species. Additionally, the PUFA compositions of white adipose tissue (WAT) samples taken from individuals in the field were identical, indicating that diet PUFA contents for these two species were also equivalent. Therefore, while high PUFA diets can enhance hibernation by these species, it does not appear to explain the differences between spontaneous and facultative strategies. The rate of lipid peroxidation during torpor, however, was significantly higher in the WAT from white-tailed prairie dogs. Ancestral prairie dog species are spontaneous hibernators. Natural selection may have favored shallow, facultative hibernation with lower lipid peroxidation rates in the black-tailed prairie dogs as they radiated from the Rocky Mountains into the Great Plains.

Protein use and muscle-fiber changes in free-ranging, hibernating black bears.

Studies of the metabolic and physiological changes that bears undergo during hibernation have, for the most part, supported the paradigm that bears use only fatty tissues as a metabolic substrate during hibernation. This study was performed to document the extent of protein loss and alteration of muscle-fiber characteristics of selected muscles in black bears during winter dormancy. Muscle biopsies were removed from the gastrocnemius and biceps femoris from seven free-ranging female black bears on the Uncompahgre Plateau in west-central Colorado. Six of the seven bears produced cubs during the hibernating season. Muscle samples were collected from the left hind limb shortly after bears entered their dens (fall), and additional samples were collected from the right hind limb just prior to bears leaving their dens (spring). Protein concentration, fast- and slow-twitch muscle-fiber ratios and muscle-fiber cross-sectional areas, and citrate synthase activity were measured in the laboratory. While protein concentration decreased in both muscles during the hibernation period, it was lower than predicted for lactating females. In addition, muscle-fiber number and cross-sectional area were unchanged in these muscles, suggesting only limited muscle atrophy. In support of these observations, there was a moderate but significant increase in the proportion of fast-twitch fibers only in the biceps femoris, with a concomitant decrease in citrate synthase activity, but no alteration of the fiber ratio in the gastrocnemius during hibernation. These findings suggest that hibernating bears, particularly lactating females, do use some protein, in concert with fat catabolism, as a metabolic substrate and as a source of water. However, the extent of this protein use is moderate and is associated with limited alteration of muscle structure, characteristic of disuse atrophy.

Gastric Na+K+ATPase activity and intestinal urea hydrolysis of the common vampire bat, Desmodus rotundus.

The blood diet of the vampire bat represents an extraordinarily high ratio of protein to other nutrients and the highest water consumption per body weight of any other mammal. This bat has a unique gastrointestinal morphology that is characterized by a reduced small intestine, absence of a large intestine and intestinal cecum and the presence of a water-absorptive gastric fundus. The present study demonstrates that the gastric fundus has a greater Na+K+ATPase activity for active ion transport compared with other equally sized mammals. This activity is believed to be necessary to establish a gradient favoring water absorption across what would otherwise be an osmotic disequilibrium. The absence of a large intestine and intestinal cecum may reflect a reduced urea hydrolysis by the vampire bat. The present study demonstrated that the vampire bat does not hydrolyze urea as does an equally sized non-sanguinivorous mammal. These data suggest that the blood diet and the relocation of water-absorptive tissue from the lower intestinal tract to the stomach is associated with an active ion transport mechanism in the gastric tissue and a reduced capacity for ureolytic microbes to hydrolyze urea in the intestine. Both processes are specializations for a diet high in protein and water.

Hibernation-induction trigger. I. Opioid-like effects of prairie dog plasma albumin on induced contractility of guinea pig ileum.

Studies have shown that plasma albumin fractions (PAFs) from hibernating mammals can inhibit induced contractility of the guinea pig ileum similarly to morphine. This study examined PAFs from two species of prairie dogs, one that undergoes natural seasonal hibernation (white-tailed, WT) and one that does not but can be induced to hibernate (black-tailed, BT). Dose-response curves of lyophilized PAF yielded IC50 values (mg) of 20.23 for summer WT, 15.53 for hibernating WT, 15.45 for summer BT, and 13.16 for winter-active BT. Winter samples from both species have IC50s lower than samples from summer animals, indicating greater potency of winter PAFs in suppressing guinea pig ileum contractility and therefore the presence of more opioid ligands in winter prairie dog plasma. Studies to elucidate receptor selectivity of PAF continue.

Hibernation-induction trigger. II. In vitro effects of prairie dog plasma albumin on mouse vas deferens contractility.

Involvement of opioid molecules in hibernation is well established, with the delta opioid receptor implicated in hibernation induction. Previous studies have shown that plasma albumin fractions (PAFs) from hibernating mammals contain an uncharacterized ligand called "hibernation-induction trigger" (HIT), which causes inhibition of induced contractility in the guinea pig ileum (GPI). In part I of this study, we described effects of PAF from two species of prairie dogs on induced contractility of the GPI. In the present study (part II), we examine the response of the mouse vas deferens (MVD), which is populated with the delta receptor subtype, to increasing concentrations of PAF from the white-tailed prairie dog (WT) and the black-tailed prairie dog (BT). Dose-response curves of lyophilized PAF yielded IC50 values (mg) (mean dose that inhibits contractility to 50% of control) of 11.0 for summer WT, 10.6 for hibernating WT, 9.4 for summer BT, 12.2 for winter active BT, and 4.7 for winter hibernating BT. These results suggest that delta opioid (HIT) is present in both species throughout the calendar year and that the induction of hibernation may involve not only levels of opioid but also dynamic interactions between endogenous opioid and its receptors.

Thermoregulatory responses of the North American porcupine (Erethizon dorsatum bruneri) to decreasing ambient temperature and increasing wind speed.

Average resting metabolic rate of five adult male porcupines (Erethizon dorsatum bruneri) was 0.23 ml O2/g.h +/- 0.007 SEM, between 10 degrees C (Tlc) and 25 degrees C, which is 70% of the value predicted by body mass. A Tb of 37.1 degrees C +/- 0.1 SEM was maintained between -10 degrees C and 25 degrees C. Calculated thermal conductance (between 6 degrees C and -10 degrees C) was 87% of the predicted value. There was no significant change in mean metabolic rate as a function of wind (up 4.3 m/s) at ambient temperatures (1 degree C and -5 degrees C) below their Tlc. Under these same ambient conditions, with and without wind, the skin surface and subcutaneous areas of the porcupine's rosette region exhibited marked temperature lability.

Annual cycle of plasma testosterone in male copperheads, Agkistrodon contortrix (Serpentes, Viperidae): relationship to timing of spermatogenesis, mating, and agonistic behavior.

Reproductive cycles of the majority of squamate reptiles remain undescribed. Few studies are available on seasonal patterns of circulating steroid hormones in snakes. The goal of this study was to document the annual cycle of plasma testosterone (T) in male copperheads Agkistrodon contortrix, a North American pitviper (Serpentes, Viperidae). Two experimental conditions were used in this laboratory study. One condition (repeat-test group) consisted of 10 adult males that were sampled once each month for 11 months. The other condition (single-test groups) consisted of 10 groups each with 5 males (N = 50), and each male was tested a single time. The single-test condition was used to evaluate whether or not repeated handling and sampling affected T levels. The study was conducted from February-December, 1992. A well-defined seasonal pattern of plasma T levels was detected; patterns were similar under both experimental conditions with the exception that the repeat-test group had slightly lower levels. Levels of T were lowest (baseline) in April-May, increased in early summer (June), and were highest in late summer (August). Thereafter, T levels declined up to the time of hibernation (early November) and changed little during hibernation (November-January). Upon emergence from hibernation in late winter (February), T levels increased sharply from February to March and then decreased from March to April. The results are discussed in the context of timing of spermatogenesis, mating, and male agonistic behavior.

Levels of plasma corticosterone and testosterone in male copperheads (Agkistrodon contortrix) following staged fights.

Fighting behavior between male copperheads (Agkistrodon contortrix) occurs during the two mating periods (late summer/fall and spring) to gain priority of access to females. Fights are characterized by prominent vertical challenge displays, swaying, and a high degree of physical contact that does not involve biting. At the moment of subordination, losers retreat quickly from fights and winners respond by chasing. Subsequently, losers do not participate in further challenge displays or fighting for at least 7 days, and also they show behavioral signs of stress, which includes submissive acts and suppression of sexual behavior. The goal of this study was to determine whether or not losers show elevated levels of plasma corticosterone (B) and depressed levels of plasma testosterone (T) relative to winners and controls. Winners and losers were produced in 13 staged trials. Two different controls (N = 26) were run. Males with no recent agonistic experience were (1) tested in the fighting arena in the absence of a competitive male but paired with a single female (N = 13), and (2) tested alone in their cages (N = 13). All trials, including controls, were conducted in spring and late summer. Mean B in losers at 1-hr postfight was significantly greater than in winners and both control groups in both seasons. Mean T was significantly greater in late summer in all groups, as expected, but in each season was not significantly different between the groups. Levels of B and T were not correlated with SVL, mass, or duration of fighting. This study provides further support for the social insensitivity/challenge hypotheses and is the first to document postfight B and T levels in snakes.

Kidney structure and function of obligate and facultative hibernators: the white-tailed prairie dog (Cynomys leucurus) and the black-tailed prairie dog (Cynomys ludovicianus).

The white-tailed prairie dog is an obligate hibernator that enters a heterothermic phase when maintained in the cold with low intensity light and ad libitum food and water. The black-tailed prairie dog (a facultative hibernator) will not hibernate under similar conditions. It has been suggested that the black tailed prairie dog remains active during the winter because it can conserve water more effectively due to a more efficient kidney. The present study revealed no significant differences between the species in renal morphology: relative medullary thickness, nephron heterogeneity, renal vasculature, or fornix dimensions, all of which are structures associated with the urinary concentrating mechanism. In addition, there was no difference in number of nephrons between the two species. The black-tailed prairie dog does produce a more concentrated urine when food and water deprived. However, this difference was not observed when the animals were salt loaded. The water-deprivation and salt-loading experiments suggest that the higher urine osmolality produced by the back-tailed prairie dog during fasting is a result of a higher urea load due to a greater protein catabolism and not because of a differential capacity to concentrate urine.

Effects of eimerian (Apicomplexa: Eimeriidae) infections on nutrient assimilation in the Wyoming ground squirrel.

Effects of infection with mixed species of Eimeria (E. callospermophili, E. morainensis, and E. beecheyi) on the digestive physiology of Wyoming ground squirrels (Spermophilus elegans) are described. Infected and uninfected squirrels were administered arginine and methionine in saturated glucose solution. Blood was drawn at time 0 and 30 min postadministration. Significant differences were not found between infected and uninfected squirrels in plasma glucose, arginine, or methionine assimilation. In a second experiment, infected and uninfected squirrels were fed a food slurry of known caloric value. All feces were collected for 24 hr postfeeding. Differences were not detected in fecal caloric content or digestive efficiency. These results in conjunction with results reported in the literature suggest a reassessment of the "parasitic" nature of these squirrel symbionts. We propose that associations of some Eimeria species and hosts that evolve under natural conditions are examples of parasite-host interactions that often evolve toward commensalism.

Seasonal serum urea-creatinine ratios in wild and captive American badgers, Taxidea taxus.

1. Blood samples were taken from 22 American badgers in the field during different seasons and analysed for urea and creatinine. 2. The urea-creatinine ratio (U/C) of these animals did not decrease during the winter as previously reported for black bears. This suggests that the badger, unlike the bear, does not demonstrate a winter physiological state of protein conservation. 3. This may be the consequence of intermittent ingestion of protein by the badger during the winter, or due to biochemical mechanisms unique to the bear which allows for protein turnover and resynthesis. 4. Captive badgers fasted in the laboratory during the winter also did not exhibit lower U/C ratios and protein catabolism, compared to a summer fast, thereby supporting the latter hypothesis that badgers do not have an adjustment in protein catabolism during the winter season.

Altered tyrosine and tryptophan metabolism during hypothermic hibernation in the 13-lined ground squirrel (Spermophilus tridecemlineatus).

(1) Tyrosine and tryptophan metabolism in brain and peripheral tissues were studied in hypothermic hibernating and normothermic nonhibernating 13-lined ground squirrels (Spermophilus tridecemlineatus). (2) In the hypothermic hibernating state, there were significant elevations of brain stem tyrosine, norepinephrine, and dopamine levels; forebrain norepinephrine and dopamine levels; and cerebellum norepinephrine and tyrosine levels. (3) On the other hand, plasma norepinephrine levels were significantly decreased in hypothermic hibernating squirrels while plasma tyrosine levels were increased. Kidney norepinephrine levels were significantly increased in hypothermic hibernating squirrels, while kidney tyrosine levels were decreased. Total plasma tryptophan and free plasma tryptophan were significantly reduced in hypothermic hibernating squirrels. Hepatic tyrosine aminotransferase Km and Vmax were decreased in hypothermic hibernating squirrels, while tryptophan 2,3-dioxygenase activity was not altered. Plasma and liver albumin were increased in hypothermic hibernating squirrels, while plasma and liver total protein were not altered. (4) These results demonstrate that significant changes in tyrosine and tryptophan metabolism occur in both central and peripheral tissues with concomitant alterations in metabolites during hypothermic hibernation in 13-lined ground squirrels.

Influence of the pineal gland and melatonin on blood flow and evaporative water loss during heat stress in rats.

Plasma melatonin levels of laboratory rats were elevated both during acute heat exposure (43 degrees C for 40 min) and chronic exposure (33 degrees C for 17 days) suggesting a possible correlation between melatonin and thermoregulatory mechanisms. Pinealectomy reduced the nighttime elevation in oxygen consumption and evaporative water loss. In addition, pinealectomized animals exhibited a significantly lower cutaneous evaporative water loss both at night and during the day when exposed to an acute heat exposure of 38 degrees C for 45 min. Pinealectomy elevated the blood pressure over the control group whereas melatonin infusion depressed the blood pressure without altering the cardiac output. This relationship implies an action by melatonin on the peripheral vasculature. In support of this conclusion, melatonin pretreatment tended to dampen the vasopressive effect of infused norepinephrine. These data, therefore, suggest a role of the pineal gland and melatonin in thermoregulation through an influence on the cardiovascular system and evaporative water loss.

The influence of cholecystokinin octapeptide and angiotensin II on in vitro duodenal motility in hibernating and aroused 13-lined ground squirrels.

Because cholecystokinin octapeptide and angiotensin II are directly involved in intestinal food and water absorption, the effect of these two compounds on intestinal motor responses of hibernating and alert 13-lined ground squirrels was investigated. Both cholecystokinin octapeptide and angiotensin II caused a greater increase in the composite motility of intestinal segments of normothermic in contrast to hypothermic hibernating ground squirrels. Additionally, cholecystokinin caused an increase in the contraction frequency of the intestine from normothermic as compared to hypothermic squirrels. This differential response may provide an adaptive advantage by decreasing food and water consumption; depressing motility and inhibiting digestive enzyme release; reducing the release of bile which also may have an irritant effect on the intestinal mucosa under prolonged exposure. As a result, the GI tract is devoid of food and digestive enzyme irritants during torporous periods.

Epithalamus of the nine-banded armadillo, Dasypus novemcinctus.

The epithalamus of embryonic, neonatal and adult nine-banded armadillo (Dasypus novemcinctus) was examined for evidence of pineal-like tissue. The evagination of the diencephalic roof (the anlage of the epiphysis) was not found in any embryonic specimens. In the adult brain, the epithalamus is dominated by the sub-commissural organ (SCO) which is surrounded entirely by the posterior commissure. At the most caudal aspect of the SCO, previous investigators have observed pineal-like tissue. Using pineal-specific staining techniques however, we found no evidence of this tissue. Because the armadillo produces melatonin in a rhythmic manner, exhibits exacting circadian rhythms, and shows altered rhythms when exposed to exogenous melatonin, we believe other organs, perhaps the retina or Harderian gland, must be involved in maintaining the coordinated melatonin titer.