Biosynthesis of fatty acids by the carp, Cyprinus carpio L., in relation to environmental temperature

The incorporation of unsaturated fatty acids of the n-9, n-6, and n-3 families into individual phospholipids by isolated hepatocytes of thermally-acclimated rainbow trout, Salmo gairdneri

Rates of incorporation of 1-14C-oleic (18:1n9), -linoleic (18:2n6), and -linolenic (18:3n3) acids into individual phosphatides were determined in isolated hepatocytes from cold (5 degrees C)- and warm (20 degrees C)-acclimated rainbow trout, Salmo gairdneri. Fatty acid incorporation into phosphatidylcholine (PC) exceeded that into all other phospholipids, but at assay and acclimation temperatures of 5 degrees C, incorporation into phosphatidylethanolamine (PE) was generally intermediate between that of PC and the remaining phosphatides. Specific radioactivities (ratios of percentage isotope incorporation-to-mole percentage of phosphatide) were consistently less than one for both PC and PE, and greater than one for phosphatidic acid (PA), lysophosphatidylcholine (LPC), phosphatidylserine (PS), and cardiolipin (CL). For PS, specific radioactivities were greater in cold- than warm-acclimated trout, and greater at 5 degrees C than 20 degrees C. Rates of oleate incorporation were generally higher, and rates of incorporation of 18:2 and 18:3 lower in cold- than warm-acclimated trout. Most phospholipids demonstrated a clear preference for the incorporation of 18:2 when assayed at 20 degrees C; however, at 5 degrees C the incorporation of 18:2 was reduced and 18:3 was generally the preferred substrate. A reduction in assay temperature from 20 degrees C to 5 degrees C also shifted the incorporation of 18:2 away from PC into PS and PA. These data were interpreted to indicate 1) a cold-induced activation of PS metabolism, possibly resulting in elevated levels of PE; 2) lower rates of general acyl group turnover in animals acclimated to 5 degrees C than 20 degrees C; 3) a specificity to the acclimation response that favors the incorporation at cold temperatures of polyunsaturated fatty acids, but not the parent acids from which they are derived; and 4) the participation of a deacylation-reacylation cycle in the metabolism of phospholipids, particularly at cold temperatures.

Influence of temperature, environmental salinity and fasting on the patterns of fatty acids synthesized by gills and liver of the european eel (Anguilla anguilla)

A rise in temperature on the average from 8 to 28 degrees C resulted in an enhanced relative incorporation of [1-14C]acetate into saturated fatty acids in liver tissue. The same effect was seen in gill tissue, but only after incubation in vitro and when the precursor was injected into the eel. When [1-14C]acetate was added to the water in the incubation tank such a "homeoviscous adaption" was not observed in gill tissue. A rise in temperature resulted in less relative incorporation of radioactivity into saturated gill fatty acids. We attribute this difference to a specific labelling of salt transport cells in the gills, due to the labelled precursor itself taking part in biological ion transport when it is added to the water. It would appear that palmitoleic acid plays a special role in the function of the salt transport cell. When [1-14C]acetate was added to the water in the incubation tank there was a significantly enhanced percentage incorporation into saturated gill fatty acids in fresh water relative to sea water. Fasting led to less relative incorporation of [1-14C]acetate into saturated liver fatty acids in vitro.

Influence of environmental temperature on mitochondrial membranes

Mitochondrial phospholipids from goldfish lateral line muscle were analysed with respect to polar and apolar groups. Groups of 20 goldfish, acclimated to 5, 20 and 30 degrees C, were used. Temperature-induced shifts of both polar and apolar groups of the mitochondrial phospholipids were observed. The fatty acid composition of mitochondrial phospholipids is characterized by a large amount of polyenoic acids, dominated by docosahexaenoic acid and by octadecadienoic acid. At the higher acclimation temperatures, a significant decrease in docosahexaenoic acid is found. However, the resultant effect of environmental temperature on the degree of unsaturation is small, in contrast to the marked effect on mean chain length. Pronounced changes in the molar ratio of phosphatidylcholine and phosphatidylethanolamine are seen; a decrease in mitochondrial phosphatidylcholine is observed at low acclimation temperature, which is compensated for by a nearly equal increase in phosphatidylethanolamine. The main phospholipids are, apparently, phosphatidylcholine, phosphatidylethanolamine and cardiolipin, comprising 90% of the total pool of 12 species. It is found that the anionic nature of the phospholipids is increased at low acclimation temperatures. We discuss this effect and its probable importance in the stabilization of the surface potential of the mitochondrial membranes.

The effect of hibernation on the positional distribution of ethanolamineglycerophospholipid fatty acids in hamster brain membranes

Microsomal and myelin membrane fractions were prepared from the brains of warm-adapted (room temperature) and hibernating Syrian Hamsters (Mesocricetus auratus). Ethanolamineglycerophospholipids were isolated and subjected to a fractionation scheme to separate the fatty acids of the plasmenylethanolamine and the phosphatidylethanolamine 1 and 2 positions. The major changes in microsomal phosphatidylethanolamine with hibernation were relative increases in 18:1 at the 1 position and 20:4(n-6) in the 2 position. In myelin, 18:1 increased and 18:0 decreased at the 1 position while the 2 position showed an increase in 16:0 and a decrease in 22:6(n-3). Plasmenylethanolamine fatty acids also changed in microsomes and myelin although the magnitudes were not as great and confined to longer chain fatty acids. In both membranes, fatty acid alterations were position-specific, and no new types of fatty acids were introduced at any position.

Fatty acid and sterol synthesis by hepatocytes of thermally acclimated rainbow trout (Salmo gairdneri)

Incorporation of tritium from tritiated water into lipid fractions was measured in isolated hepatocytes from rainbow trout (Salmo gairdneri) acclimated to 5 degrees C and 20 degrees C. Hepatocytes from cold-acclimated trout exhibited significantly higher rates of tritium incorporation into both fatty acid and sterol fractions at assay temperatures of 15 degrees C and 20 degrees C than did hepatocytes from warm-acclimated trout. Tritium incorporation into the fatty acid fraction was nearly temperature independent in hepatocytes from warm-acclimated trout (Q10 = 1.39) but markedly temperature dependent (Q10 = 2.63) in hepatocytes from cold-acclimated trout; in contrast, rates of sterol synthesis were more temperature dependent in warm-acclimated trout. At 5 degrees C, fatty acid lipogenesis comprised a significantly greater percentage of the total tritium incorporation in hepatocytes from warm-acclimated trout and the percentage of total lipogenesis attributable to fatty acids decreased significantly in warm-acclimated trout as the assay temperature increased; the opposite trends were observed in cold-acclimated trout.