Frederic Decrock's research while affiliated with Institut Pluridisciplinaire Hubert Curien and other places

During starvation, after a short dynamic period of adaptation (phase I), a metabolic steady state is reached in which proteins are spared and lipids provide most of the energy expended [phase II (P2)]. However, protein breakdown increases dramatically once a lower threshold of body lipids is reached [phase III (P3)]. Body composition, energy intake, energy expenditure, and energy efficiency were determined in 8 groups of rats (fed, food-deprived up to P2 or P3 of starvation and refed for 3 d, 7 d, or until body mass restoration) to determine whether the kinetics of lipid and/or protein reserve recovery may be slowed down when refeeding occurs after the lipid threshold has been reached. Despite larger losses, P3 refed rats restored their body reserves as efficiently as those refed in P2. Whatever the nutritional status at the onset of refeeding, rehydration occurred first and hyperphagia played a more important role than hypometabolism in the restoration of the lost reserves. However, the pattern of body component gains was different during early refeeding. In P3 refed rats, body lipids were restored preferentially by significant contribution from endogenous lipid production. Thus, the extent of lipid depletion has important consequences for the restoration pattern of the body reserves. It depends not only on the intensity of the energy restriction (partial or total) as already demonstrated but also on the metabolic status at the onset of refeeding. These results may have significant implications on the way refeeding should be conducted after severe energy depletion.

In fasting-incubating seabirds, it has been proposed that egg abandonment and refeeding should be induced when a low body mass (BM) threshold is attained, thus ensuring adult survival at the expense of immediate breeding. In the context of life-history trade-offs in long-lived birds, we have tested this hypothesis by comparing short-term survival and restoration of BM in King Penguins Aptenodytes patagonicus that abandoned their egg to those that were relieved normally by their mate at the end of the first incubation shift. Since King Penguins have an extended laying period, the possible influence of seasonal factors was also examined by comparing early and late breeders. Forty incubating males were experimentally forced to fast until egg abandonment by preventing relief by the female. At egg abandonment of both early and late breeding males, BM was below the BM threshold, fasting duration was eight days (about 30%) longer than for relieved birds, and plasma uric acid level was elevated (signature of increased body protein catabolism, phase III of fasting). All abandoning birds survived and came back from sea at a BM similar to that of relieved penguins. The duration of the foraging trip of abandoning early breeders was the same as that of relieved birds, and some abandoning birds engaged in a new breeding attempt. Abandoning late breeders, however, made foraging trips twice as long as those of relieved males. This difference can be explained by time constraints rather than nutritional constraints, abandoning early breeders having enough time left in the breeding season to engage in a new breeding attempt in contrast to abandoning late breeders. These observations lend support to the suggestion that not only BM but also an internal clock intervene in the decision to engage in breeding or not. By preventing a lethal energy depletion ashore and by acting at a fasting stage where the capacity to restore BM at sea is unaffected, abandonment at a low body condition threshold plays a major role in the trade-off between adult penguin survival and reproduction.

This study examines the metabolic fate of total and individual yolk fatty acids (FA) during the embryonic development of the king penguin, a seabird characterized by prolonged incubation (53 days) and hatching (3 days) periods, and a high n-3/n-6 polyunsaturated FA ratio in the egg. Of the approximately 15 g of total FA initially present in the egg lipid, 87% was transferred to the embryo by the time of hatching, the remaining 13% being present in the internalized yolk sac of the chick. During the whole incubation, 83% of the transferred FA was oxidized for energy, with only 17% incorporated into embryo lipids. Prehatching (days 0-49), the fat stores (triacylglycerol) accounted for 58% of the total FA incorporated into embryo lipid. During hatching (days 49-53), 40% of the FA of the fat stores was mobilized, the mobilization of individual FA being nonselective. At hatch, 53% of the arachidonic acid (20:4n-6) of the initial yolk had been incorporated into embryo lipid compared with only 15% of the total FA and 17-24% of the various n-3 polyunsaturated FA. Similarly, only 32% of the yolk's initial content of 20:4n-6 was oxidized for energy during development compared with 72% of the total FA and 58-66% of the n-3 polyunsaturated FA. The high partitioning of yolk FA toward oxidization and the intense mobilization of fat store FA during hatching most likely reflect the high energy cost of the long incubation and hatching periods of the king penguin. The preferential partitioning of 20:4n-6 into the structural lipid of the embryo in the face of its low content in the yolk may reflect the important roles of this FA in tissue function.

Because the yolk lipids of the king penguin (Aptenodytes patagonicus) contain the highest concentrations of long-chain n-3 polyunsaturated fatty acids yet reported for an avian species, the consequences for the establishment of the brain's fatty acid profile in the embryo were investigated. To place the results in context, the fatty acid compositions of yolk lipid and brain phospholipid of the king penguin were compared with those from three other species of free-living birds. The proportions of docosahexaenoic acid (22:6n-3; DHA) in the total lipid of the initial yolks for the Canada goose (Branta canadensis), mallard (Anas platyrhynchos), moorhen (Gallinula chloropus), and king penguin were (% w/w of fatty acids) 1.0+/-0.1, 1.9+/-0.2, 3.3+/-0.1, and 5.9+/-0.2, respectively. The respective concentrations of DHA (% w/w of phospholipid fatty acids) in brains of the newly hatched chicks of these same species were 18.5+/-0.2, 19.6+/-0.7, 16.9+/-0.4, and 17.6+/-0.1. Thus, the natural interspecies diversity in yolk fatty acid profiles does not necessarily produce major differences in the DHA content of the developing brain. Only about 1% of the amount of DHA initially present in the yolk was recovered in the brain of the penguin at hatch. There was no preferential uptake of DHA from the yolk during development of the king penguin.

Since the yolk lipids of the king penguin (Aptenodytes patagonicus) naturally contain the highest concentrations of DHA and EPA yet reported for the eggs of any avian species, the effects of this (n-3)-rich yolk on the FA profiles of the embryonic heart and skeletal muscle were investigated. The concentrations (mg/g wet tissue) of phospholipid (PL) in the developing heart and leg muscle of the penguin doubled between days 27 and 55 from the beginning of egg incubation (i.e., from the halfway stage of embryonic development to 2 d posthatch), whereas no net increase occurred in pectoral muscle. During this period, the concentration of TAG in heart decreased by half but increased two- and sixfold in leg and pectoral muscle, respectively. The most notable change in cholesteryl ester concentration occurred in pectoral muscle, increasing ninefold between days 27 and 55. Arachidonic acid (ARA) was the major polyunsaturate in PL of the penguin's heart, where it formed about 20% (w/w) of FA at day 55. At the equivalent developmental stage, the heart PL of the chicken contained a 1.3-fold greater proportion of ARA, contained a fifth less DHA, and was almost devoid of EPA, whereas the latter FA was a significant component (7% of FA) of penguin heart PL. Similarly, in PL of leg and pectoral muscle, the chicken displayed about 1.4-fold more ARA, up to 50% less DHA, and far less EPA in comparison with the penguin. Thus, although ARA-rich PL profiles are achieved in the heart and muscle of the penguin embryo, these profiles are significantly affected by the high n-3 content of the yolk.

To investigate the importance of body fuel depletion on gut rehabilitation after food deprivation, we compared the kinetics of jejunal mucosa alteration and restoration in rats that were refed after reaching different stages in body fuel depletion. Rats (P2) were refed while still in the so-called phase II, where body protein utilization is minimized, whereas rats (P3) were refed when they had reached the stage of increasing protein utilization (phase III). There was a significant decrease in total mass of intestine (P2, −30%; P3, −40%) and jejunal mucosa (P2, −52%; P3, −60%), as well in the size of the crypts (P2, −15%; P3, −36%) and villi (P2, −37%; P3, −55%). Structural changes of the mucosa included disappearance of some villi and a reduction in the size and number of crypts. Despite the larger morphological alterations in P3, the restoration of mucosa was as fast and complete after only 3 days of refeeding for both P2 and P3 rats. The respective roles of the mitosis pressure and of the lamina propria dynamics were studied. The rapid reversibility of the gut mucosal alterations due to fasting might constitute an integrative process.

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.

This study examines the transfer of lipids from the yolk to the embryo of the king penguin, a seabird with a high dietary intake of n-3 fatty acids. The concentrations of total lipid, triacylglycerol (TAG), and phospholipid (PL) in the yolk decreased by ~80% between days 33 and 55 of development, indicating intensive lipid transfer, whereas the concentration of cholesteryl ester (CE) increased threefold, possibly due to recycling. Total lipid concentration in plasma and liver of the embryo increased by twofold from day 40 to hatching due to the accumulation of CE. Yolk lipids contained high amounts of C(20-22) n-3 fatty acids with 22:6(n-3) forming 4 and 10% of the fatty acid mass in TAG and PL, respectively. Both TAG and PL of plasma and liver contained high proportions of 22:6(n-3) ( approximately 15% in plasma and >20% in liver at day 33); liver PL also contained a high proportion of 20:4(n-6) (14%). Thus both 22:6(n-3) and 20:4(n-6), which are, respectively, abundant and deficient in the yolk, undergo biomagnification during transfer to the embryo.

This study is directed toward understanding the process of feeding stimulation ("refeeding signal") that has been suggested to operate below a body mass threshold or critical metabolic status in spontaneously fasting birds. Behavior and egg temperature (T(egg)) were continuously monitored by video monitoring and biotelemetry, respectively, in fasting-incubating king penguins kept in a pen to prevent relief by the partner until spontaneous egg abandonment. Penned birds fasted 10 days more and lost 1.2 kg more than birds relieved normally by their partner, abandoning the egg about 1 wk after reaching a critical body mass. Definitive egg abandonment was preceded by transitory abandonments of progressively increasing duration during which time the birds went further and further away from their egg. There were marked interindividual differences but on average transitory abandonments began 36 +/- 5 h before the definitive abandonment and were paralleled by resumption of display songs signaling the readiness of the bird to depart for feeding. T(egg) was maintained at around 35.7 degrees C during normal incubation but significantly decreased the last 2 days before egg abandonment. These changes are interpreted as reflecting a stimulation to refeed at a threshold body mass corresponding to a critical fat store depletion. Thus the fasting-incubating king penguin appears to be an interesting animal model for understanding the long-term metabolic control of feeding behavior in relation to energy status.

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.