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R Groscolas

Publications and source records attributed to R Groscolas.

At least 37 records · Page 2Linked to original sources
PubMed1995

Selectivity of fatty acid mobilization: a general metabolic feature of adipose tissue.

This study extends our earlier work (T. Raclot and R. Groscolas. J. Lipid Res. 34: 1515-1526, 1993), which showed that, under norepinephrine-stimulated lipolysis, fatty acids of rat retroperitoneal fat cells are selectively mobilized. The present study examines whether this selective mobilization of fatty acids 1) is based on their proportions in adipose tissue, 2) is a metabolic feature common to all adipose tissues, and/or 3) depends on the lipolysis-stimulating agent. Rat fat cells with two markedly different fatty acid compositions were isolated from four white adipose tissues and treated with three lipolytic agents. Fatty acid composition of in vitro released free fatty acids was compared with that of fat cell triacylglycerols, the ratio of percent in free fatty acid to percent in triacylglycerol being defined as the relative mobilization rate (RMR). The RMR of individual fatty acids was related to their molecular structure. It increased exponentially with unsaturation for a given chain length and decreased with increasing chain length for a given unsaturation. The selectivity of fatty acid mobilization was similar regardless of the fatty acid composition of adipose tissue, the tissue location, and the lipolytic agent used. Under conditions of stimulated lipolysis, the selectivity of fatty acid mobilization is therefore a general metabolic feature of adipose tissue. Fatty acids with 16-20 carbon atoms and 4 or 5 double bonds had the highest RMR (from 1.4 to > 5), whereas fatty acids with 20-22 carbon atoms and 0 or 1 double bond had the lowest RMR (from 0.3 to 0.7). For the other fatty acids, RMR was close to unity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Deaminase↗
PubMed1995

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.

Adipocytes↗
PubMed1994

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)

Adipose Tissue, Brown↗
PubMed1994

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.

Adipose Tissue↗
PubMed1993

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)

Adipose Tissue↗
PubMed1993

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)

Abdomen↗
PubMed1993

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)

Adipose Tissue↗
PubMed1989

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.

Animals↗
PubMed1988

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.

Animals↗
PubMed1988

Protein and lipid utilization during long-term fasting in emperor penguins.

The body mass of male emperor penguins is approximately 38 kg at the beginning of the 4-mo winter fast connected with breeding, and it is an estimated approximately 18 kg in leanest birds at time of spontaneous refeeding. For a 38- to 18-kg range, we investigated the changes in the rate of body mass loss, body composition, and plasma concentrations of uric acid and urea. After the first few days (phase I) a steady state (phase II) was reached in the proportions of the energy derived from proteins and lipids with proteins accounting for a constant 4%, and the remaining 96% being from lipids. The same proportions were maintained until body mass had decreased to 24 kg. Below this value the proportion of energy derived from proteins increased progressively (phase III), being 14 times higher at 18 kg than during phase II. Rate of body mass loss and plasma uric acid and urea concentrations closely reflected the changes in protein utilization: being at a low and steady value throughout phase II and increasing during phase III. Emperor penguins also fast during the spring, but for periods of only 2-3 wk. We found a 2.5 times higher value for rate of body mass loss, uric acid, and urea during spring phase II, suggesting lower effectiveness in protein sparing at that time. It may be attributed to the lower initial lipid reserves of spring birds. Would these findings be generalized to the wide variety of birds and mammals that spontaneously fast under natural conditions?(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1986

The endocrine control of reproduction and molt in male and female emperor (Aptenodytes forsteri) and adelie (Pygoscelis adeliae) penguins. I. Annual changes in plasma levels of gonadal steroids and LH.

Changes in plasma LH, testosterone, and estrogens were investigated throughout reproduction and molt in free-living male and female emperor (Aptenodytes forsteri) and adelie (Pygoscelis adeliae) penguins. In both sexes and species, plasma LH and gonadal steroids were severalfold above basal level at the time of arrival on the breeding grounds, suggesting that environmental cues (especially decreasing daylength in emperors) rather than mating and courting primarily stimulate gonadal development and reproduction. In both species a marked increase in plasma LH (both sexes), testosterone (males), and estrogens (females) corresponded with the time of maximum gonadal size, and peak values were obtained at the time of copulation, i.e., in emperors about 10-15 days prior to egg laying. In females, plasma LH and estrogens dropped to low levels between copulation and egg laying. Similarly, following copulation in males plasma testosterone fell to lower levels that in emperors were maintained during incubation and brooding of the non-thermally emancipated chick. Plasma LH levels followed the same trend as testosterone, falling after copulation and falling further prior to molt. Though lower than at copulation, plasma LH was higher in incubating (males) and brooding (males and females) emperors than during rearing of the thermally emancipated chicks, suggesting that plasma LH might be related to incubating, brooding, and territorial behavior. In male and female emperors and in male adelies, plasma gonadal steroids and LH were at basal levels throughout molt.

Animals↗
PubMed1986

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.

Animals↗
PubMed1982

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.

Animals↗
PubMed1980

Resting metabolic rate and cost of locomotion in long-term fasting emperor penguins.

During the Antarctic winter emperor penguins fast for up to 120 days when breeding at rookeries, which may be as much as 120 km from open water. Emperors have lost almost half of their body mass by the time they walk back to the sea to feed. Resting metabolic rate and metabolic rate during treadmill walking at 1.4 km times h-1 were measured regularly along the course of 63-118 days of fasting in four emperors that lost between 33 and 55% of their body mass. Resting metabolic rate decreased linearly with body mass throughout the fast; it was 76 and 50 W at 39 and 18 kg body mass, respectively, which therefore corresponds to a limited increase in the resting metabolic rate per unit of body mass. There was a considerable decrease in the metabolic rate for walking at 1.4 km times h-1, from 340 to 140 W at body masses of 39 and 18 kg, respectively; this decrease was linear with body mass but at a steeper rate below 23 kg. From 39 to 23 kg, the cost of walking per unit of body mass remained constant. Below 23 kg (a point where about 2.5 kg of fat remain), the increased efficiency for walking may be due to a change in the mechanics of locomotion.

Adipose Tissue↗
PubMed1976

[Use of energy reserves during the breeding fast of the emperor penguin, Aptenodvtes 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.

Adipose Tissue↗
PubMedDate not supplied

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.

Animals↗