Heart rate as a predictor of energy expenditure in undisturbed fasting and incubating penguins.

Heart rate (f(H)) measurement offers the possibility to monitor energy expenditure (EE) in wild animals if the EE/f(H) relationship for the species, physiological stages and activities of interest is known. This relationship has been extensively studied using oxygen consumption rate ( ) measurement in captive, repeatedly handled king penguins (Aptenodytes patagonicus). Unfortunately, the potential effects of stress on the observed relationships resulting from handling and confinement were not considered. This study is the first involving undisturbed animals, and determines the EE/f(H) relationship in naturally fasting and freely incubating or captivity-acclimatized male and female king penguins. EE determination was based on (1) the measurement of body mass loss during periods of phase II fasting, and (2) the calculation of its energy equivalent from changes in body composition, i.e. 23.9 kJ g(-1). f(H) levels in freely incubating and captivity-acclimatized birds were found to be 50-70% lower than those previously reported for resting king penguins during measurements. Significant EE/f(H) relationships were found in freely incubating and captive males and females (R(2)=0.59 to 0.84), with no difference observed between genders. The best overall relationship was obtained by including fasting duration (t, days) in the model: EE=818+43.7xf(H)+36.3t-1.4txf(H) (R(2)=0.91). This equation yielded EE estimates approximately 26% higher than the previously reported 'best' predictive equation in king penguins, and even more so when f(H) was low. This result suggests that stress induces a disproportionate increase of f(H) vs O(2) consumption, and that the use of EE/f(H) relationships obtained in stressed birds could lead to underestimated EE values.

Individual fish-oil n-3 polyunsaturated fatty acid deposition and mobilization rates for adipose tissue of rats in a nutritional steady state.

The storage in and mobilization from rat adipose tissue of 20:5n-3, 22:6n-3, 22:5n-3, and 18:4n-3 fatty acids were investigated. After fish-oil feeding, substantial amounts of these fatty acids were stored in fat depots. However, the in vivo relative incorporation (% in triacylglycerols/% in diet) increased significantly in this order: 20:5n-3 (0.25) < 18:4n-3 (0.37) < 22:6n-3 (0.49) < 22:5n-3 (0.78). The in vitro relative mobilization (% in free fatty acids/% in triaclyglycerols) decreased significantly in this order: 20:5n-3 (2.88) > 18:4n-3 (1.51) > 22:6n-3 (1.08) > 22:5n-3 (0.91). Similar results were obtained from rats maintained on a low-fat control diet. Dietary essential n-3 polyunsaturated fatty acids are therefore selectively mobilized from fat stores, which could explain their selective storage. The preferential mobilization of eicosapentaenoic acid could contribute to its maintenance in the circulation after fish-oil feeding, but it probably limits its postintake long-term storage.

Lipid composition of blood platelets and erythrocytes of southern elephant seal (Mirounga leonina) and antarctic fur seal (Arctocephalus gazella).

Erythrocyte and blood platelet phospholipid compositions were studied in three elephant seals and two fur seals, two species of marine mammals living in the Subantarctic region feeding on preys rich in (n-3) polyunsaturated fatty acids. Results were compared with those reported for related species and humans. In erythrocytes, the phospholipid (PL) and cholesterol (CHOL) contents were lower in pinnipeds than in humans. Phosphatidylcholine (PC) levels were higher in elephant seals than in fur seals, with a reverse trend for phosphatidylethanolamine (PE) and phosphatidylserine (PS). Both species had lower SM/PC ratios and PE plasmalogen concentrations than human. Erythrocytes were richer in (n-3) fatty acids (FA) in pinnipeds than in humans. In platelets, the PL content was lower and the CHOL content higher in elephant seals than in humans or in other phocid seal species studied to date. The SM/PC ratio was much higher than in other seal species or in man. In both species, the proportion of PE plasmalogens was higher in platelets than in erythrocytes. PL were more saturated in elephant seals than in fur seals. These results suggest that the erythrocytes and platelets of wild marine mammals may prove useful models to study the influence of dietary lipids on the structure and hemostatic function of these cells.

Composition and structure of triacylglycerols in brown adipose tissue of rats fed fish oil.

This study examines the incorporation of highly unsaturated n-3 fatty acids (HUFA) into triacylglycerols (TAG) of brown adipose tissue (BAT), and their effect on the positional distribution of saturated (SFA) and of unsaturated (UFA) 16- or 18-carbon fatty acids. To this end, rats were fed a fish oil diet for up to four weeks. The stereospecific analysis of TAG was based on generation of sn-1,2- and sn-2,3-acylglycerols by Grignard degradation, followed by synthesis of phosphatidic acid and specific hydrolysis with phospholipase A2. From the end of the first week of fish oil feeding, a steady-state in the fatty acid composition of TAG in BAT was reached. HUFA concentration increased 30-fold, mainly at the expense of n-9 UFA and of SFA. The amount of SFA decreased selectively at position 3, where these fatty acids were progressively replaced by n-3 HUFA. By contrast, the amount of UFA decreased at all positions, and their positional distribution was not affected. About 60% of HUFA was incorporated at position 3. Nearly twice as much 22:6n-3 was incorporated into TAG than had been previously observed in white adipose tissue (WAT) [Leray, C., Raclot, T., and Groscolas, R. (1993) Lipids 28, 279-284]. At the steady-state, the distribution of HUFA was characterized by high proportions of 22:6n-3 and 20:5n-3 in position 3. Moreover, in each position of TAG, a steady level was reached rapidly (within 1 wk).(ABSTRACT TRUNCATED AT 250 WORDS)

Positional distribution of n-3 fatty acids in triacylglycerols from rat adipose tissue during fish oil feeding.

The present study was designed to investigate the metabolism of the n-3 polyunsaturated fatty acids (PUFA) in adipose tissue and its dependence upon dietary factors. Changes in the positional distribution of the fatty acids in triacylglycerols from retroperitoneal adipose tissue were studied as a function of time on rats fed for 4 wk a diet enriched with fish oil. The stereospecific analysis of triacylglycerols by Grignard degradation. This was followed by synthesis of rac-phosphatidic acids and treatment with phospholipase A2. In the triacylglycerols of the fish oil diet, 57% of the total n-3 fatty acids were in position 3, i.e., two-thirds of 20:5n-3 and 22:5n-3 were esterified in sn-3 position, whereas 22:6n-3 was equally distributed in positions 2 and 3. After 4 wk of feeding fish oil, the fatty acid composition of adipose tissue triacylglycerols reached a steady state. Half of the n-3 fatty acids were found in position 3, namely 75% of 22:5n-3, 50% of 20:5n-3 and 18:4n-3 and 45% of 22:6n-3, the latter being equally distributed in positions 2 and 3. This pattern of distribution resembled that found in triacylglycerols of the fish oil diet, except for a higher proportion of 20:5n-3 in adipose tissue in position 1 at the expense of position 3. Throughout the 4-wk period of fish oil feeding, the distribution pattern of minor n-3 fatty acids (18:4n-3 and 22:5n-3) in adipose tissue triacylglycerols remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acid composition of the adipose tissue and yolk lipids of a bird with a marine-based diet, the emperor penguin (Aptenodytes forsteri).

The emperor penguin (Aptenodytes forsteri) is an Antarctic seabird feeding mainly on fish and therefore has a high dietary intake of n-3 polyunsaturated fatty acids. The yolk is accumulated in the developing oocyte while the females are fasting, and a large proportion of the fatty acid components of the yolk lipids are derived by mobilization from the female's adipose tissue. The fatty acid composition of the total lipid of the yolk was characterized by high levels of n-3 polyunsaturated fatty acids. However, it differed in several respects from that of the maternal adipose tissue. For example, the proportions of 14:0, 16:1n-7, 20:1n-9, 22:1n-9, 20:5n-3, and 22:6n-3 were significantly greater in adipose tissue than in yolk. Thus adipose tissue lipids contained 7.6+/-0.3% and 8.0+/-0.3% (wt% of total fatty acids; mean +/- SE; n = 5) of 20:5n-3 and 22:6n-3, respectively, whereas the yolk total lipid contained 1.6+/-0.1 and 5.5+/-0.3% of these respective fatty acids. The proportions of 16:0, 18:0, 18:1n-9, 18:2n-6, and 20:4n-6 were significantly lower in the adipose tissue than in the yolk lipids. The proportions of triacylglycerol, phospholipid, free cholesterol, and cholesteryl ester in the yolk lipid were, respectively, 67.0+/-0.2, 25.4+/-0.3, 5.3+/-0.2, and 1.8+/-0.2% (wt% of total yolk lipid). The proportions of 20:4n-6, 20:5n-3, 22:5n-3, and 22:6n-3 were, respectively, 5.7+/-0.3, 2.8+/-0.2, 1.4+/-0.1, and 11.7+/-0.5% in phospholipid and 0.4+/-0.0, 1.2+/-0.1, 0.8+/-0.1 and 3.6+/-0.3% in triacylglycerol. About 95% of the total vitamin E in the yolks was in the form of alpha-tocopherol with gamma-tocopherol forming the remainder. Two species of carotenoids, one identified as lutein, were present.

Lipid composition of erythrocytes and thrombocytes of a subantarctic seabird, the king penguin.

Phospholipid (PL) compositions and fatty acid (FA) patterns of PL were determined in the erythrocytes and blood thrombocytes of a seabird, the king penguin, living in the subantarctic area and feeding on prey rich in n-3 polyunsaturated FA. Results were compared between birds in three different physiological states (breeding and molting adults, chicks) to those reported for other birds. In erythrocytes, the ratios of cholesterol to PL and of sphingomyelin to phosphatidylcholine (PC) were lower than in other birds. The PL distribution was similar to those previously reported in the hen and pigeon. In contrast to other birds, cardiolipin levels were unexpectedly high (4%). Very long chain n-3 FA were abundant (13-27%) in phosphatidylethanolamine (PE), phosphatidylserine and PC, probably in relation to the natural diet of these birds. Among n-3 FA, 22:6n-3 was the most abundant in all PL (2-20%), whereas the highest levels of arachidonic acid were observed in PE (14%). In thrombocytes, the PL distribution and FA composition of the main PL (PC, PE) differed from those of erythrocytes, and in particular, levels of n-3 FA (9-12%) were 1.5-2 times lower. The highest levels of arachidonic acid were found in phosphatidylinositol (24%). The lipid profile of penguin erythrocytes could contribute to the efficiency of blood circulation and oxygen delivery in microvascular beds, thus favoring diving capacity of these animals. Our observations do not support the hypothesis of a common origin of avian thrombocytes and erythrocytes.

Milking strategy in subantarctic fur seals Arctocephalus tropicalis breeding on Amsterdam Island: evidence from changes in milk composition.

Milk composition was investigated throughout the 10-mo pup-rearing period in subantarctic fur seals (Arctocephalus tropicalis) breeding on Amsterdam Island. The mean milk composition was 42.8% +/- 5.7% lipid, 12.1% +/- 1.5% protein, and 42.6% +/- 7.3% water. Subantarctic fur seals breeding on Amsterdam Island produced one of the richest milks ever reported in otariids (20.4 +/- 2.9 kJ/g), with lipid content contributing 85% of total gross energy. The high lipid levels measured in the milk of subantarctic fur seals breeding on Amsterdam Island is consistent (i) with the relatively long time lactating females spend at sea, due to the relatively poor local trophic conditions near the colony that necessitate that they travel long distances to reach the foraging grounds, and (ii) with the consequently short time mothers spend with their pups ashore. Milk composition changed according to the time mothers were fasting ashore: milk produced during the first 2 d spent ashore, when more than 80% of milk transfer occurred, had higher levels of lipids, proteins, and gross energy than milk produced later during the visit ashore, suggesting that the pups were fed with two types of milk during a suckling period. Throughout the year, mothers in good condition produced milk of higher lipid content than others, suggesting that individual foraging skills contribute to enhance milk quality. Milk lipid and gross energy content varied with pup age, according to quadratic relationships, increasing during the earlier stages of lactation before reaching asymptotic values when pups were 180 d old. The stage of lactation appears to be a better predictor of milk lipid content than the duration of the preceding foraging trip, suggesting that either changes in the nutritional requirements of the pup and/or seasonal changes in trophic conditions act on milk composition. These changes in milk quality may also be related to changes in maternal care; lactating subantarctic fur seals apparently reallocate their body reserves toward gestation rather than lactation at the end of the pup-rearing period.

Transfer of Vitamins E and A from yolk to embryo during development of the king penguin (Aptenodytes patagonicus).

Since the yolk lipids of the king penguin (Aptenodytes patagonicus) are rich in n-3 fatty acids, which are potentially susceptible to peroxidative damage, the yolk contents and yolk-to-embryo transfer of antioxidants and lipid-soluble vitamins were investigated under conditions of natural incubation in the wild. The concentration of vitamin E in the unincubated egg was 155 microg/g wet yolk, of which 88% was alpha-tocopherol and the rest was gamma-tocopherol. Vitamin A (2.9 microg/g) was present in the yolk entirely as retinol; no retinyl esters were detected. Throughout the latter half of the incubation period, vitamins E and A were taken up from the yolk into the yolk sac membrane (YSM) and later accumulated in the liver, with vitamin A being transferred in advance of vitamin E. In the YSM, vitamin A was present almost entirely as retinyl ester, indicating that the free retinol of the yolk is rapidly esterified following uptake. Retinyl esters were also the predominant form in the liver. The retinyl esters of the liver and YSM displayed different fatty acid profiles. At hatching, the brain contained relatively little vitamin E (4.7 microg/g) compared to the much higher concentration in the liver (482.9 microg/g) at this stage. Ascorbic acid was not detected in the yolk but was present at a high concentration in the brain at day 27 (404.6 microg/g), decreasing to less than half this value by the time of hatching. This report is the first to delineate the yolk-to-embryo transfer of lipid-soluble vitamins for a free-living avian species. The yolk fatty acids of the king penguin provide an extreme example of potential oxidative susceptibility, forming a basis for comparative studies on embryonic antioxidant requirements among species of birds whose yolk lipids differ in their degree of unsaturation.

The use of body mass loss to estimate metabolic rate in fasting sea birds: a critical examination based on emperor penguins (Aptenodytes forsteri).

1. The validity of the body mass loss (BML) method to estimate incubation and molting metabolic rate (MR) in sea birds is examined on the basis of data in emperor penguins (Aptenodytes forsteri). 2. The BML composition of emperors during mid incubation is revised (61.7% fat, 5.9% protein and 32.4% water; energy equivalent of BML = 25.5 kJ/g). 3. Using these data in short-term fasting petrels and penguins, or with BML obtained at the beginning or at the end of the fast in long-term fasting species, may lead to up to 2-fold overestimates of incubation metabolic rate (IMR). Similarly, molting MR may be overestimated by up to three times. 4. The use of the 25.5 kJ/g energy equivalent with BML obtained during middle part of the incubation shift seems valid in long-term fasting species. It is suggested that IMR within the thermoneutral zone might be close to basal MR in most antarctic and sub-antarctic sea birds.

Differential mobilization of white adipose tissue fatty acids according to chain length, unsaturation, and positional isomerism.

The present study aims at determining whether, and how, the molecular structure of fatty acids influences their mobilization from fat cells. The in vitro mobilization of 52 fatty acids ranging in chain length from 12 to 24 carbon atoms, in unsaturation from 0 to 6 double bonds, and including 23 pairs of positional isomers was examined. Fat cells were isolated from adipose tissue of rats fed a fish-oil diet and treated with norepinephrine to stimulate lipolysis. Fatty acid composition of free fatty acids (FFA) released from these cells was compared to that of the triacylglycerols (TAG) from which they originated. The percentage weight of most fatty acids, and especially that of very long-chain fatty acids, was significantly different between FFA and TAG. The percentage of 20:5n-3 (eicosapentaenoic acid) and of 20:4n-6 (arachidonic acid) was 2.7 and 1.7 times higher in FFA than in TAG, respectively, whereas that of 20:1(n-11, 9 or 7), 22:1(n-11, 9 or 7) and 24:1n-9 was 1.7-2, 2.4, and 3.5 times lower, respectively. The relative mobilization (% in FFA/% in TAG) of the least readily mobilized fatty acid (24:1n-9) was 15-fold lower than that of the most readily mobilized (18:5n-3). For a given chain length, the relative mobilization increased exponentially with unsaturation, e.g., increasing from 0.45 to 2.7 in C 20 fatty acids when the number of double bonds increased from 0 to 5. Amongst the fatty acids with 18 to 22 carbon atoms, the shorter the chain was, the more steeply relative mobilization increased with unsaturation. On the other hand, for a given unsaturation the relative mobilization decreased with increasing chain length, e.g., decreasing from 1.15 to 0.3 in monoenes when the chain length increased from C 14 to C 24. A two-carbon-atom shortening of the chain length was on average equivalent to inserting one double bond for increasing the relative mobilization, i.e., by about 40%. The relative mobilization was also affected by the position of the double bond(s); increasing on average by 10% when there was a two-carbon-atom displacement towards the methyl end of the chain. These results demonstrate that under conditions of stimulated lipolysis individual fatty acids are more readily mobilized from fat cells when they are short and unsaturated, and when their double bonds are closer to the methyl end of the chain.(ABSTRACT TRUNCATED AT 400 WORDS)

The endocrine control of reproduction and molt in male and female emperor (Aptenodytes forsteri) and adelie (Pygoscelis adeliae) penguins. II. Annual changes in plasma levels of thyroxine and triiodothyronine.

Changes in plasma thyroxine (T4) and triiodothyronine (T3) levels were studied during a breeding season and in more detail during the postbreeding molt in male and female emperor (Aptenodytes forsteri) and adelie (Pygoscelis adeliae) penguins under natural conditions in the Antarctic. During the 4-month natural fast that accompanies courtship and incubation in male emperors, plasma T4 and T3 levels were maintained around 11 and 0.6 ng/ml, respectively. In courting, fasting female emperors plasma T4 levels were maintained around 10 ng/ml for more than 1 month; plasma T3 levels were around 0.8 ng/ml but were markedly depressed (0.1 ng/ml) at the time of copulation although they increased again (2.2 ng/ml) at oviposition. During the 5-month period of chick rearing, plasma T3 (males and females) and T4 (females) were maintained at the same levels as during courtship and incubation, but plasma T4 levels in male emperors were slightly lower (7 ng/ml). Similar plasma T4 and T3 levels were observed in breeding adelie penguins. These results do not provide any convincing evidence for thyroid-gonadal interrelations in breeding penguins, but demonstrate their capacity to maintain plasma thyroid hormone levels during very prolonged natural fasts. During the heavy postnuptial molt when the birds were fasting, in both species and sexes, marked but separate peaks in plasma T4 and T3 levels occurred concurrently with the initial growth of the new feathers, and with the subsequent shedding of the old plumage, respectively. Peak plasma T4 levels were observed at the time of the emergence of the new feathers out of the skin, and peak plasma T3 levels were roughly concurrent with the maximum daily body weight loss. This is the first strong evidence that increases in plasma T4 and T3 levels are correlated with different stages of molt in a wild seabird. Increased plasma T4 but not T3 levels at the time of feather papilla eruption suggest that T4 is concerned with feather growth, but is not exclusive of a role of T3. Increased plasma T3 but not T4 levels during the reduction in thermal insulation in molting penguins suggest that this hormone rather than T4 might be active in energy metabolism in penguins.

The effect of severe starvation and captivity stress on plasma thyroxine and triiodothyronine concentrations in an antarctic bird (emperor penguin).

The effect of confinement and severe starvation on the plasma thyroxine (T4) and triiodothyronine (T3) concentrations was determined in emperor penguins (Aptenodytes forsteri). During their annual cycle, emperor penguins fast freely for periods of up to 4 months and may thus represent a unique subject to study endocrine adaptations to fasting. Plasma T4 concentrations progressively decreased following capture and confinement of naturally fasting penguins, and within 15-20 days stabilized at levels three times lower than in free-living penguins. A transient fourfold increase in plasma T3 concentration developed within the day following confinement in parallel with a rise in daily body mass loss. Both plasma T3 concentration and mass loss subsided to normal levels within 15 days. The decrease in plasma T4 concentration is in accordance with the well-known inhibitory effect of stress on thyroid function in birds and mammals, whereas the transient increase in plasma T3 concentration seems related to enhancement of energy expenditure as a consequence of restlessness. Starvation severe enough to exhaust fat stores and to activate protein catabolism induced a 6- and 5 to 10-fold fall in plasma T4 and T3, respectively. This is in marked contrast with maintenance of plasma thyroid levels during long-term natural fasting associated with protein sparing (R. Groscolas and J. Leloup (1986) Gen. Comp. Endocrinol. 63, 264-274). Surprisingly, there was a final reincrease in plasma T4 concentration in very lean penguins. These results suggest that the effect of starvation on plasma thyroid hormones seems to depend on how much protein catabolism is activated and demonstrate the acute sensitivity of thyroid hormone balance to stress in penguins.

Selective mobilization of adipose tissue fatty acids during energy depletion in the rat.

This study extends our previous work (Raclot, T., and R. Groscolas. 1993. J. Lipid Res. 34: 1515-1526) which demonstrated that in the fed state fatty acids are selectively released from white adipocytes in vitro. It aims at determining whether such selectivity operates in vivo during energy depletion and has physiological relevance. This question was examined in rats by simultaneously measuring, after 1, 7, or 10 days of fasting, the fatty acid content of retroperitoneal adipose tissue (RP), and the composition of fatty acids released by isolated RP adipocytes. A preliminary dietary manipulation (fish oil feeding) allowed us to study the mobilization of a wide spectrum of fatty acids. Fasting resulted in a relative depletion of adipose tissue in fatty acids such as alpha-linolenic, arachidonic, and eicosapentaenoic, and in a relative enrichment in all very long chain saturated and monounsaturated fatty acids. After a 56% depletion of total fatty acids, 20% (22:1n-11) to 90% (20:5n-3) of the initial mass of individual fatty acids was lost. The in vivo relative mobilization of fatty acids (% in lost fatty acids / % in RP triacylglycerols) ranged from 0.31 to 2.54. For a given chain length it increased with unsaturation whereas for a given degree of unsaturation it decreased with chain length. The in vitro relative mobilization of fatty acids (% in released fatty acids/% in RP triacylglycerols) was similarly dependent on their molecular structure and, to a significant extent, directly related to in vivo mobilization. It is concluded that during fasting-induced energy depletion, the net in vivo mobilization of fatty acids from adipose tissue is selective. The selectivity of mobilization i) is based on the molecular structure of fatty acids, ii) is fully accounted for by their selective release from adipocytes, iii) leads to a profound remodelling of the composition of adipose tissue fatty acids, and iv) does not seem directed towards a preferential retention or sparing of particular fatty acids.

[Use of energy reserves during the breeding fast of the emperor penguin, Aptenodvtes forsteri]. / Utilisation des réserves énergétiques au cours du jeûne de la reproduction chez le Manchot empereur, Aptenodytes forsteri

During the breeding fasting of the emperor penguin, the lipid and protein stores are steadily used to meet the metabolic needs; they represent respectively 93 and 7% of the energy production in the animal. The role of the glucid stores are quantitively negligible. Loss of tissue water represents 35,3% of body weight loss. Increased weight loss below 20 kg a "critical weight", is associated with a conversion to protein catabolism when lipid supplies are exhausted. These results allow the estimation of the metabolism when the body weight loss is considered in this antartic penguin.

Glucose and lactate kinetics and interrelations in an antarctic bird (emperor penguin).

The isotope single-injection method was used to investigate the glucose and lactate kinetics and the interrelationships between the glucose and lactate pools in fasting emperor penguins. In these remarkably fast-resistant birds, mean lactate concentration, replacement rate, pool, space, and transit time were 1.5 mmol.1-1,53 mumol.min-1.kg-1, 900 mumol.kg-1, 60% of body mass, and 17 min, respectively. Mean glucose concentration, replacement rate, pool, space, and transit time were 20 mmol.1-1, 23 mumol.min-1.kg-1, 4,300 mumol.kg-1, 24% of body mass, and 196 min, respectively. Maximum conversions of lactate into glucose and of glucose into lactate were 29 +/- 2.9% and 75.5 +/- 4.2%, respectively, which indicates that lactate is an effective gluconeogenic precursor and a major fate of glucose metabolism in fasting penguins. The lactate replacement rate and incorporation into glucose were related to the plasma lactate concentration, which suggests that the rate of formation of glucose from lactate is dependent on the availability of lactate. The glucose replacement rate and reduction into lactate were related with the plasma glucose concentration, suggesting that the rate of lactate formation from glucose is dependent on the plasma glucose concentration. These data suggest that in the fasting emperor penguin glucose and lactate availability is capable of regulating the rate at which these substrates are utilized and interconverted. To our knowledge, this is the first evidence for such regulatory capacities in birds.

Fish oil n-3 fatty acids selectively limit the hypertrophy of abdominal fat depots in growing rats fed high-fat diets.

Because dietary n-3 polyunsaturated fatty acids (n-3 PUFA) from fish oils have profound effects on lipid metabolism, we examined whether they influence the growth of adipose tissue at different locations in growing rats. Rats were fed for 4 wk on high-fat (HF) diets (20% fat) containing very low (L), medium (M), and high (H) amounts of n-3 PUFA but similar amounts of saturated fatty acids and n-6 PUFA. A fourth group was fed a standard laboratory diet (control group) to estimate changes in adipose tissue mass related to growth. At the end of the dietary treatment, the lipid mass (LM) of the four major adipose depots (subcutaneous, SC; mesenteric, MES; retroperitoneal, RP; epididymal, EPI) and total adiposity were significantly higher in each of the three HF groups than in the control group. The lipid gain in EPI was due to fat cell hypertrophy alone, whereas RP showed both hypertrophy and hyperplasia. Energy intake, fatty acid excretion, and body mass were the same in the three groups fed HF diets. Similarly, there was no difference in the LM or in lipid gains specifically caused by HF feeding of SC and MES between the HF groups. In contrast, the LM of RP was significantly lower in the H than in the L and M groups (50 and 30%, respectively). The LM of EPI was also 30% lower in the H than in the L group.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term fasting and re-feeding in penguins.

Spontaneous fasting during reproduction (sometimes with a full stomach) and moult is a major characteristic of the annual cycle of penguins. Long-term fasting (up to four months in male emperor penguins) is anticipated by the accumulation of fat (incubation fast) and of fat and protein (moult fast). During most of the incubation fast, birds rely almost entirely on lipids as an energy source, body proteins being spared. However, below a critical (but non-total) fat store depletion, marked behavioural, metabolic, and endocrine changes occur. Spontaneous locomotor activity increases and the egg is transitorily left unincubated for increasingly long periods, until its definitive abandon and the bird departs to re-feed at sea. These changes are thought to be activated by an endogenous re-feeding signal triggered before lethal energy depletion. An increase in body protein catabolism in the face of a reduction in lipid availability and utilisation, and an increase in circulating corticosterone vs. a decrease in plasma prolactin, are likely to be major metabolic and hormonal components of this signal. The survival and rapid restoration of energy stores in birds having departed to re-feed at a stage of near total lipid depletion demonstrates the effectiveness of the re-feeding signal. Penguins, and possibly other seabirds, are therefore appropriate animal models for understanding the long-term interactions between body energy reserves and fasting, breeding and feeding physiology and behaviour.

Fasting-induced selective mobilization of brown adipose tissue fatty acids.

This study was conducted to determine whether there is selective mobilization of fatty acids from brown adipose tissue. Rats were fed a fish-oil diet and then fasted for 0, 7, or 10 days followed by analysis of the fatty acid content and composition of triacylglycerols (TAG) and phospholipid (PL) in interscapular brown adipose tissue (IBAT). Fatty acids were selectively lost from IBAT triacylglycerols, the mobilization following the same structural rules as those previously demonstrated for white adipose tissue. Fractional mobilization increased with unsaturation at a given chain length and tended to decrease with chain length at a given unsaturation. However, linoleic acid (18:2 n-6) was mobilized significantly less than predicted by these structural rules. In IBAT phospholipid, fatty acids were also selectively lost but there was no such relationship between the fractional mobilization of a fatty acid and its structure. The fatty acids of the n-6 series were exceptional in their behavior because they displayed below average fractional mobilization. In fact, linoleic and arachidonic acids actually increased their mass in IBAT phospholipid during the fast. It is concluded that, in IBAT, fatty acids are selectively mobilized during a fast, and that fasting-induced remodeling of the fatty acid composition leads to the selective retention of linoleate in the case of TAG and all the n-6 fatty acids in the case of PL.