Prolonged fasting increases the response of the renin-angiotensin-aldosterone system, but not vasopressin levels, in postweaned northern elephant seal pups

The 8- to 12-week postweaning fast exhibited by northern elephant seal pups (Mirounga angustirostris) occurs without any apparent deleterious effects on fluid and electrolyte homeostasis. However, during the fast the role of vasopressin (AVP) has been shown to be inconclusive and the involvement of the renin-angiotensin-aldosterone system (RAAS) has yet to be examined. To examine the effects of prolonged fasting on these osmoregulatory hormones, 15 postweaned pups were serially blood-sampled during the first 49 days of their fast. Fasting did not induce significant changes in ionic or osmotic concentrations, suggesting electrolyte homeostasis. Total proteins were reduced by day 21 of fasting and remained depressed, suggesting a lack of dehydration. Aldosterone and plasma renin activity exhibited a correlated, linear increase over the first 49 days of the fast, suggesting an active RAAS. Aldosterone exhibited a parabolic trend over the fast with a peak at day 35, suggesting a shift in the sensitivity of the kidney to aldosterone later in the fast. AVP was elevated at day 49 only, but concentrations were relatively low. RAAS was modified during the postweaning fast in pups and appears to play a significant role in the regulation of electrolyte and, most likely, water homeostasis during this period.     

5'AMP-activated protein kinase activity is increased in adipose tissue of northern elephant seal pups during prolonged fasting-induced insulin resistance

Northern elephant seals endure a 2- to 3-month fast characterized by sustained hyperglycemia, hypoinsulinemia, and increased plasma cortisol and free fatty acids, conditions often seen in insulin-resistant humans. We had previously shown that adipose Glut4 expression and 5'AMP-activated protein kinase (AMPK) activity increase and plasma glucose decreases in fasting seals suggesting that AMPK activity contributes to glucose regulation during insulin-resistant conditions. To address the hypothesis that AMPK activity increases during fasting-induced insulin resistance, we performed glucose tolerance tests (GTT) on early (n=5) and late (n=8)-fasted seal pups and compared adipose tissue expression of insulin signaling proteins, peroxisome proliferator-activated receptor γ (PPARγ), and AMPK, in addition to plasma adiponectin, leptin, cortisol, insulin, and non-esterified fatty acid (NEFA) levels. Fasting was associated with decreased glucose clearance, plasma insulin and adiponectin, and intracellular insulin signaling, as well as increased plasma cortisol and NEFAs, supporting the suggestion that seals develop insulin resistance late in the fast. The expression of Glut4 and VAMP2 increased (52 and 63% respectively) with fasting but did not change significantly during the GTT. PPARγ and phosphorylated AMPK did not change in the early fasted seals, but increased significantly (73 and 50% respectively) in the late-fasted seals during the GTT. Increased AMPK activity along with the reduction in the activity of insulin-signaling proteins supports our hypothesis that AMPK activity is increased following the onset of insulin resistance. The association between increased AMPK activity and Glut4 expression suggests that AMPK plays a greater role in regulating glucose metabolism in mammals adapted to prolonged fasting than in non-fasting mammals.     

Re-alimentation in harbor seal pups: Effects on the somatotropic axis and growth rate

The metabolic hormones, growth hormone (GH) and insulin-like growth factor (IGF)-I, together with IGF binding proteins (IGFBP), have been well studied in domestic species and are the primary components of the somatotropic axis. This hormone axis is responsive to nutrient intake, associated with growth rate, and accretion of protein and adipose. However, this relationship has not been evaluated in species that rely heavily on adipose stores for survival, such as pinnipeds. The primary objectives of this research were to investigate the response of the somatotropic axis to reduced nutrient intake and re-alimentation in rehabilitated harbor seal pups, and to assess if these hormones are related to nutritional status and growth rate in harbor seals. Stranded harbor seal pups (n = 24) arrived at the rehabilitation facility very thin after fasting for several days (nutritional nadir). Throughout rehabilitation nutrient intake increased and pups gained mass and body condition. Concentrations of GH and IGFBP-2 decreased with re-alimentation, while IGF-I and IGFBP-3 concentrations increased. Overall, GH and IGFBP-2 were negatively associated and IGF-I and IGFBP-3 were positively associated with growth rate and increased body condition of harbor sea pups. Further, the magnitude of the growth response was related to the magnitude in response of the somatotropic axis to varied levels of intake. These data suggest that multiple components of the somatotropic axis may be used to assess the energy status of individuals and may also provide information on the level of feed intake that is predictive of growth rate.     

Effects of hypoxia and hypercapnia on aerobic metabolic processes in northern elephant seals.

An hypoxia-induced metabolic down-regulation has been implicated as an important protective mechanism against tissue deoxygenation in mammals. Whether the same response to hypoxia occurs in northern elephant seals was studied. The effects of hypercapnia were also examined to determine whether the reduced ventilatory response of seals to CO2 is associated with an analogous protective metabolic down-regulation. Thirty three seals (7-300-days-old) were studied using open-flow respirometry with simultaneous monitoring of apnea frequencies and heart rates. Hypoxia (11% O2) and hypercapnia (7% CO2) caused increases in metabolism of up to 38% with corresponding decreases in the percent time spent apneic (%AP) and increases in heart rate. The metabolic, breathing and heart rate responses to altered inspired gases were independent of age. Metabolism was strongly negatively correlated with %AP suggesting that elevated metabolism during hypoxia and hypercapnia exposure is attributable to decreases in %AP. In young elephant seals metabolic down-regulation is not an automatic protective response to experimentally-imposed hypoxia or hypercapnia.     

GH and ghrelin increase with fasting in a naturally adapted species,the northern elephant seal (Mirounga angustirostris)

After nursing, pups of the northern elephant seal (Mirounga angustirostris) are approximately 46% body fat and rely almost entirely on the oxidation of their large fat stores to sustain their metabolism for the ensuing 8-12 week postweaning fast, which is a natural component of their life history. Thus, fasting pups provide an ideal opportunity to examine the hormonal alterations associated with prolonged food deprivation in a naturally adapted model. Cortisol, ghrelin, glucagon, growth hormone (GH), insulin-like growth factor-I (IGF-I), insulin, blood urea nitrogen (BUN), glucose and non-esterified fatty acids (NEFA) were examined in 20 male and 20 female pups blood sampled early (<1 week postweaning) and late (6-8 weeks postweaning) during the fast. Mean cortisol, ghrelin, GH, and glucagon increased 1.8-, 1.8-, 1.4-, and 2.3-fold between early and late periods, while mean IGF-I and insulin decreased 97% and 38%, respectively. NEFA increased 2.3-fold, while BUN and glucose decreased 46% and 11%, respectively. NEFA was significantly and positively correlated with cortisol and GH; individually; however, when the relationship was examined as a multiple regression the correlation improved suggesting that cortisol and GH act synergistically to promote lipolysis during the fast. GH and BUN were negatively and significantly correlated between early and late fasting suggesting that GH may promote protein sparing as well. The decrease in glucose may be responsible for stimulating glucagon, resulting in the maintenance of relative hyperglycemia. The increases in cortisol, ghrelin, glucagon, and GH suggest that these hormones may be integral in mediating the metabolism of seal pups during prolonged fasting.     

Holocene elephant seal distribution implies warmer-than-present climate in the Ross Sea

We show that southern elephant seal (Mirounga leonina) colonies existed proximate to the Ross Ice Shelf during the Holocene, well south of their core sub-Antarctic breeding and molting grounds. We propose that this was due to warming (including a previously unrecognized period from approximately 1,100 to 2,300 (14)C yr B.P.) that decreased coastal sea ice and allowed penetration of warmer-than-present climate conditions into the Ross Embayment. If, as proposed in the literature, the ice shelf survived this period, it would have been exposed to environments substantially warmer than present.     

Plasma cortisol and thyroid hormone concentrations in pre-weaning Australian fur seal pups

The hormonal factors that influence development from birth to weaning in otariid seals is still largely unknown. In the present study, a suite of thyroid hormones and cortisol were measured in Australian fur seal pups in order to determine baseline concentrations as well as to describe their endocrinology over this critical developmental period. A cross-section of newborn pups from a breeding colony located on Kanowna Island, Australia were sampled at six different times over the course of the 10 month lactation period. Sample times were designed to correspond to periods of heightened physiological change during pre-weaning development: post-natal, pre-molt, the initiation of molt, mid-molt, period of peak milk intake and weaning. Results indicate that the greatest hormonal changes were associated with the post-natal stage and molt, with molt showing the greatest changes, as has been reported for several species of pinnipeds. Two forms of thyroid hormones analyzed (Total T₄, and Free T₃), increased with the initiation of the molt, and Free T₃ exhibited a second increase that was associated with the period of peak milk intake. The T₃:T₄ ratio was significantly lower during the initiation of molt than either pre- or mid-molt. The study was able to describe physiological change during the first year of life in Australian fur seals as well as document basal concentrations of thyroid hormones and cortisol in pups of this species.     

From the Cover: Mercury offloaded in Northern elephant seal hair affects coastal seawater surrounding rookery

Methylmercury (MeHg) is a potent neurotoxin that is biomagnified approximately 1–10 million-fold in aquatic carnivores such as the Northern elephant seal (Mirounga angustirostris), whose excreta and molted pelage, in turn, constitute a source of environmental MeHg contamination at the base of marine food chains. The potential for this top-down contamination is greatest in coastal areas with productive marine ecosystems that provide ideal habitats for large marine mammal colonies that can number in the thousands. This recycling of MeHg was evidenced by comparing total mercury (HgT) and MeHg concentrations in seawater, and HgT in molted pelage of M. angustirostris, at the Año Nuevo State Reserve pinniped rookery with concentrations at neighboring coastal sites in Central California. Seawater MeHg concentrations around the rookery (average = 2.5 pM) were markedly higher than those at the comparison coastal sites (average = 0.30 pM), and were as high as 9.5 pM during the M. angustirostris molting season. As a consequence, excreta and molts from this marine mammal colony, and presumably other marine predator populations, constitute a major source of MeHg at the base of the local marine food chain.Anthropogenic emissions have increased global atmospheric mercury (Hg) deposition to the oceans three- to fivefold since preindustrial times (1, 2). Although more than 95% of industrial and natural inputs are inorganic forms of Hg [e.g., Hg(0) and Hg(II)], a small fraction of inorganic Hg is converted by microbial activity to methylmercury (MeHg), an organic neurotoxin that readily bioaccumulates in marine organisms and biomagnifies in food chains (3–5). As a result, MeHg concentrations in high-trophic predators (i.e., piscivorous fish, birds, and marine mammals) can reach levels that are physiologically detrimental to them and that constitute a human health threat (6, 7).Although most “hot spots” of contamination in coastal waters are associated with local industrial inputs, the highest Hg concentrations initially detected in California’s Mussel Watch program four decades ago (1977–1978) were at Año Nuevo State Reserve (Fig. 1) (8). Año Nuevo hosts a relatively remote, protected rookery for a multitude of pinniped species including Northern elephant seals (Mirounga angustirostris), harbor seals (Phoca vitulina), Northern fur seals (Callorhinus ursinus), California sea lions (Zalophus californianus), Steller sea lions (Eumetopias jubatus), and Guadalupe fur seals (Arctocephalus townsendi). The average (mean ± 1 SD) Hg concentration in mussels (Mytilus californianus) at Año Nuevo was 2.50 ± 0.52 µg⋅g⁻¹ dry weight (wt.) (8). This value was 5–35 times greater than Hg concentrations in mussels collected from 42 other locations along the west coast of the continental United States (0.07–0.55 µg⋅g⁻¹ dry wt.). The exceptionally high Hg levels in mussels were tentatively attributed to the excreta of marine mammals colonizing Año Nuevo because of the relatively high Hg concentrations found in California sea lion feces (0.80 µg⋅g⁻¹) collected at the site (8). However, that attribution could not be substantiated because of the technical inability to accurately measure Hg concentrations in seawater in the 1970s (9).Open in a separate windowFig. 1.Nearshore seawater sampling locations. (A) Locations of Año Nuevo and comparison sites along the Central California coast. (B) Detailed map showing the sampling stations at the south end of the Año Nuevo mainland breeding rookery during the 2012 Northern elephant seal molting season (M1–M6) and 2013 breeding season (B1–B6), as well as the Cove Beach Año Nuevo State Reserve sampling site.The objective of this study was to test the fundamental hypothesis of top-down Hg contamination by comparing total Hg (HgT) and MeHg concentrations in nearshore seawater at the mainland Northern elephant seal rookery at Año Nuevo South Beach with those of seawater from comparison sites not affected by large marine mammal populations (Fig. 1). In addition, Northern elephant seal molted pelage was analyzed for HgT to determine whether the sloughed-off integument represented a potential source of Hg to the local ecosystem.     

The shifting baseline of northern fur seal ecology in the northeast Pacific Ocean

Historical data provide a baseline against which to judge the significance of recent ecological shifts and guide conservation strategies, especially for species decimated by pre-20th century harvesting. Northern fur seals (NFS; Callorhinus ursinus) are a common pinniped species in archaeological sites from southern California to the Aleutian Islands, yet today they breed almost exclusively on offshore islands at high latitudes. Harvest profiles from archaeological sites contain many unweaned pups, confirming the presence of temperate-latitude breeding colonies in California, the Pacific Northwest, and the eastern Aleutian Islands. Isotopic results suggest that prehistoric NFS fed offshore across their entire range, that California populations were distinct from populations to the north, and that populations breeding at temperate latitudes in the past used a different reproductive strategy than modern populations. The extinction of temperate-latitude breeding populations was asynchronous geographically. In southern California, the Pacific Northwest, and the eastern Aleutians, NFS remained abundant in the archaeological record up to the historical period approximately 200 years B.P.; thus their regional collapse is plausibly attributed to historical hunting or some other anthropogenic ecosystem disturbance. In contrast, NFS populations in central and northern California collapsed at approximately 800 years B.P., long before European contact. The relative roles of human hunting versus climatic factors in explaining this ecological shift are unclear, as more paleoclimate information is needed from the coastal zone.     

海豹油对家兔实验性动脉粥样硬化的影响

研究海豹油对家兔血脂、脂质过氧化及动脉粥样硬化斑形成的影响。方法：用喂饲高胆固醇食物和猪油的办法建立16只家兔动脉粥样硬化模型，随机分为海豹油组（高脂词料＋海豹油）和对照组（高脂饲料）。结果：连续给药8周后，海豹油组较对照组总胆固醇、甘油三酯显著降低（P＜0．01，＜0．05），高密度脂蛋白、超氧化物歧化酶显著升高（P＜0．01）。结论：海豹油对心血管病防治和康复具有重大意义。     

Breathing frequencies of northern elephant seals at sea and on land revealed by heart rate spectral analysis

Elephant seals breathe episodically at sea and on land and surprisingly long apnoeas occur in both situations. An important difference is that recovery from apnoeic periods is much quicker at sea, which might be due, in part, to differences in the ventilatory response. Respiratory frequencies of juvenile northern elephant seals diving at sea and resting on land were estimated from time-frequency maps of the Wigner distribution of heart rate variability. Simultaneous direct measurement of respiration and estimation of respiratory frequency (fR) in the laboratory demonstrated that the error of estimation was small (mean +/- S.D.= 1.05+/-1.23%) and was independent of the magnitude of fR. Eupnoeic fR at sea was 2.4 times higher than on land (22.0+/-2.0 vs. 9.2+/-1.3 breaths min(-1), respectively), facilitating quick recovery from the preceding dive and allowing a 34% increase in time spent apnoeic at sea versus on land. The overall fR (no. of breaths in a eupnoea divided by the total time of the apnoea+eupnoea cycle) of 2.3+/-0.6 breaths min(-1) at sea was no different from the rate on land and was inversely related to the preceding dive duration, suggesting that metabolism on longer dives may be reduced.     

Liver and spleen volume variations in patients with hepatic fibrosis

AIM： To study the liver and spleen volume variations in hepatic fibrosis patients at different histopathological stages.
METHODS： Multidetector computed tomography （MDCT） scan was performed in 85 hepatic fibrosis patients. Liver volume （LV） and spleen volume （SV） were measured. Fifteen healthy individuals served as a control group （SO）. The patients were divided into stage 1 （S1） group （n = 34）, stage 2 （S2） group （n = 25）, stage 3 （S3） group （n = 16）, and stage 4 （S4） group （n = 10） according to their histopathological stage of liver fibrosis.
RESULTS： The LV and standard LV （SLV） had a tendency to increase with the severity of fibrosis, but no statistical difference was observed in the 5 groups （LV： F = 0.245, P = 0.912; SLV： F = 1.902, P = 0.116）. The SV was gradually increased with the severity of fibrosis, and a statistically significant difference in SV was observed among the 5 groups （P 〈 0.01）. The LV/SV ratio and SLV/SV ratio were gradually decreased with the aggravation of hepatic fibrosis, and statistically significant differences in both LV/SV and SLV/SV were found among the 5 groups （P 〈 0.01）.
CONCLUSION： The absence of obvious LV reduction in patients with chronic liver disease may be a morphological index of patients without liver cirrhosis. The SV is related to the severity of fibrosis, and the spleen of patients with advanced fibrosis is enlarged evidently. The LV/SV ratio and SLV/SV ratio are of a significant clinical value in the diagnosis of advanced liver fibrosis.     

Role of the spleen in endotoxin-induced hepatic injury in chronic alcohol-fed rats

ABSTRACT— The present experiments were designed to study the role of the spleen in endotoxin-induced hepatic injury in chronic alcohol-fed rats. Administration of 2 mg/kg body weight of endotoxin caused severe hepatic injury in chronic alcohol-fed rats as compared with controls. This injury was significantly less in those whose spleens had been resected 1 week prior to endotoxin administration. There were no differences in plasma endotoxin levels 16 h after intravenous injection of endotoxin between sham-operated control rats, and chronic alcohol-fed rats with and without splenectomy. The plasma tumor necrosis factor (TNF) level 1 h after intravenous injection of endotoxin was significantly higher in chronic alcohol-fed rats than in controls. However, TNF levels were significantly lower in those with splenectomy. Neutrophil infiltration was seen in the liver sinusoid of sham-operated chronic alcohol-fed rats as early as 1 h after injection of endotoxin, and was observed even 15 h later. These results suggest that endotoxin-induced liver injury is closely related to factors derived from the spleen and induced by plasma endotoxin, especially when Kupffer cell function is reduced by chronic alcohol feeding. In addition, TNF and neutrophils may play an important role in this type of liver injury.     

Serum leptin concentration during the terrestrial phase of the Southern elephant seal Mirounga leonina (Carnivora: Phocidae)

This study aimed to verify the serum leptin concentration during the terrestrial phase of the Southern elephant seal (Mirounga leonina) on Elephant Island (South Shetlands, Antarctica). Sera from 25 adult Southern elephant seals were analyzed. Leptin concentration was determined using the 125I radioimmunoassay method. Total protein, triglycerides, and cholesterol concentration were measured by spectrophotometric methods. Seals were grouped by sex and their physiological status (reproducing or molting seals). In reproducing seals, serum concentrations of leptin, total protein, triglycerides, and cholesterol were, respectively, 9.33+/-1.97 ng/ml, 6.87+/-0.09 g/dl, 98.26+/-2.12 mg/dl, and 232.17+/-41.18 mg/dl in males and 5.30+/-1.36 ng/ml, 6.44+/-0.29 g/dl, 109.01+/-3.34 mg/dl, and 219.20+/-26.65 in females (mean+/-1 SD). In molting seals, these values were 2.35+/-1.51 ng/ml, 7.42+/-0.25 mg/dl, 321.10+/-20.01 mg/dl, and 244.66+/-22.24 mg/dl in males and 2.94+/-1.89 ng/ml, 7.88+/-0.46 mg/dl, 197.54 mg/dl, and 224.55+/-16.70 mg/dl in females. In both males and females, there were no significant differences (P>0.05) in total protein and cholesterol concentration between reproducing and molting seals. However, both males and females showed higher leptin concentration (P<0.05) and lower triglyceride concentration (P<0.05) in the reproductive period than in the molt period. In the reproductive period, it was expected that the Southern elephant seal shows an inhibited hunger sensation, mobilizes stored energy, and stimulates the HPG axis. Results from the present study support this hypothesis and suggest that this strategy may be effected by the hormonal stimulation of leptin.     

Effects of amiodarone on sinus node in man

The effects of amiodarone on the sinuatrial node were studied in 24 patients after an intravenous injection of the drug (5 mg/kg). Sinuatrial function was assessed by rapid atrial pacing and premature atrial stimulation. Sinus cycle length did not change significantly, but the corrected sinus node recovery time was prolonged. While there was no significant change in sinuatrial conduction time, prolongation of the non-reset zone in 14 cases, as well as the abolition of the platesu in 2/24 patients, suggested that conduction of the atrial responses to the sinus node might have been depressed.     

Role of the spleen in endotoxin-induced hepatic injury in chronic alcohol-fed rats.

The present experiments were designed to study the role of the spleen in endotoxin-induced hepatic injury in chronic alcohol-fed rats. Administration of 2 mg/kg body weight of endotoxin caused severe hepatic injury in chronic alcohol-fed rats as compared with controls. This injury was significantly less in those whose spleens had been resected 1 week prior to endotoxin administration. There were no differences in plasma endotoxin levels 16 h after intravenous injection of endotoxin between sham-operated control rats, and chronic alcohol-fed rats with and without splenectomy. The plasma tumor necrosis factor (TNF) level 1 h after intravenous injection of endotoxin was significantly higher in chronic alcohol-fed rats than in controls. However, TNF levels were significantly lower in those with splenectomy. Neutrophil infiltration was seen in the liver sinusoid of sham-operated chronic alcohol-fed rats as early as 1 h after injection of endotoxin, and was observed even 15 h later. These results suggest that endotoxin-induced liver injury is closely related to factors derived from the spleen and induced by plasma endotoxin, especially when Kupffer cell function is reduced by chronic alcohol feeding. In addition, TNF and neutrophils may play an important role in this type of liver injury.     

Effects of digitalis on sinus nodal function in patients with sick sinus syndrome

The effect on sinus rhythmicity and automaticity of complete digitalization in a 24 hour period was observed in 14 patients with sick sinus syndrome. Sinus nodal function was evaluated in these patients by assessing sinus nodal recovery time and by treadmill exercise testing and 24 hour Holter monitoring, before and after digoxin administration. Corrected sinus nodal recovery times ranged from 240 to 2,065 msec (average 714) before digoxin and were shortened to 250 to 1,260 msec (average 565) after the glycoside. Further, digoxin induced accelerated infra sinus escape pacemaker activity in five patients: junctional and ventricular in one and atrial in four. Spontaneous sinus rate evaluated with Holter monitoring revealed an average of 56 beats/min (range 43 to 69) before digitalis that was unchanged (average 58 beats/min; range 48 to 74) after digoxin therapy. Similarly, the sinus nodal response to exercise was unaffected after digitalization (average 118 beats/min both before and during digitalis therapy). It is concluded that digoxin does not exert adverse effects on sinus nodal function in patients with sick sinus syndrome. The glycoside can be used safely in these patients when indicated for cardiac pump dysfunction or for control of tachyarrhythmia.