Relationship of phosphatidylcholine to hydrophobic surfactant on rat intestinal chylomicron secretion.

Hydrophobic surfactants such as Poloxalene inhibit triglyceride secretion into lymph by enterocytes. The inhibitory effect of these agents on triglyceride secretion is reversed when lipid presented for absorption is exclusively in the form of phosphatidylcholine (PC) and not triglyceride. The present investigation performed in conscious mesenteric lymph fistula rats was designed to determine whether various mixtures of triglyceride and PC given intraduodenally with Poloxalene would also reverse the inhibitory effect of Poloxalene on triglyceride secretion into lymph. A 50-50 mixture of triolein (TO) and PC resulted in normal triglyceride secretion into lymph. However, when the mixture of lipids was 75-25, TO to PC, results for triglyceride recovery in lymph were considerably reduced. The transport rate for triglyceride into lymph was not as depressed, however, as observed for Poloxalene treated rats given lipid for absorption basically in the triglyceride form. Substitution of phosphatidylethanolamine for PC had no beneficial effect on triglyceride secretion in Poloxalene treated rats. It is concluded that PC can reverse the inhibitory effect of Poloxalene on triglyceride secretion into lymph even when considerable amounts of triglyceride along with PC are presented for absorption.

Effect of heparin on increased pulmonary microvascular permeability after bone marrow embolism in awake sheep.

We examined the alterations in pulmonary transvascular fluid and protein exchange after intravenous infusion of fat emboli, i.e., bone marrow suspension (BMS) in awake sheep prepared with chronic lung lymph fistulas and compared these changes with those observed in sheep pretreated with heparin. The BMS injection (0.2 ml/kg) over 15 min caused rapid, but transient, increases (p less than 0.05) in mean pulmonary artery pressure and pulmonary vascular resistance. These increases were accompanied by significant increases in the lymph concentrations of thromboxane B2 and 6-keto-PGF1 alpha. Pulmonary lymph flow increased by 3.9-fold (+/- 0.8) over baseline by 120 min after BMS with no change in the lymph-to-plasma protein concentration ratio (L/P ratio). Heparin pretreatment (700 U/kg) enhanced the BMS-induced increases in pulmonary artery pressure and pulmonary vascular resistance. Thromboxane B2 concentrations in the lymph increased, whereas there was no change in the concentration of 6-keto-PGF1 alpha. Lung lymph flow increased 4-fold (+/- 1.0) over baseline by 120 min after BMS without a change in L/P ratio. Changes in lung vascular permeability were evaluated by elevating pulmonary microvascular pressure (left atrial balloon catheter inflation) at 120 min after BMS. Lung lymph flow increased 7-fold (+/- 1.1) from baseline, whereas the L/P ratio decreased to a mean value of 0.48 +/- 0.03. The protein reflection coefficient (sigma = 1 - L/P ratio) decreased from a control mean of 0.69 +/- 0.02 to 0.52 +/- 0.03 after the BMS challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of essential fatty acid deficiency on pulmonary alveolar macrophage function.

Male rats were maintained for periods of up to 16 weeks on a fat free diet which was supplemented with either 4% tripalmitin (essential fatty acid [EFA] deficient) or with 4% safflower oil (SAFF, control). Pulmonary alveolar macrophages (PAM) were obtained by lung lavage. PAM from EFA deficient rats had reduced phagocytic activity and capacity. Intracellular killing of ingested yeast was also reduced by EFA deficiency. The activity of acid phosphatase, beta-glucuronidase and cathepsin D from PAM was not altered by dietary treatment. Transmission electron microscopy failed to show any consistent morphologic differences between PAM from EFA deficient and SAFF animals, but did confirm the decreased phagocytosis by PAM from EFA deficient rats. However, scanning electron microscopy did show loss of pseudopodia in PAM from EFA deficient rats. EFA deficiency was demonstrated by analyzing the methyl esters of the fatty aids from the total lipid extract of PAM. The arachidonate content was decreased while the eicosatrienoate content was increased in PAM derived from rats fed the EFA deficient diet. In an effort to elucidate further the mechanism of action of EFA deficiency in impairing phagocytosis by PAM, inhibitors of various reactions which lead to oxygenated derivatives of arachidonate were studied using PAM from chow fed rats. Some of these inhibitors were effective in diminishing phagocytosis. Furthermore, PAM from these preparations when fixed in suspension and examined with scanning electron microscopy showed morphological changes similar to those seen in EFA deficiency. This similarity of surface ultrastructural changes suggests that EFA deficiency may impair phagocytic function of PAM by reducing availability of an oxygenated derivative of arachidonic acid.

Desaturation of endogenous and exogenous palmitate in lung tissue in vitro.

lung slices from rats fed a fat-free diet supplemented with safflower oil (control) or tripalmitoylglycerol (essential fatty acid [EFA]-deficient) were incubated with [14C]acetate, [14C]palmitate, or [14C]stearate. Of the 14C recovered in phospholipids after incubation with [14C]acetate, more than 87% was in 16-carbon fatty acids. Desaturation, as assayed by the percentage of radioactivity in monoenoates in phospholipid fatty acids, was generally double in EFA-deficient slices compared to control slices, regardless of substrate. Desaturation was significantly greater in slices incubated with with acetate or octanoate compared to palmitate, indicating that endogenously synthesized palmitate was desaturated more actively than that derived from an exogenous source.

Fatty acid desaturation in lung: inhibition by unsaturated fatty acids.

The activity of the enzyme system involved in desaturation of palmitic and stearic acid has been examined in lungs of rats fed fat-free diets supplemented either with 4% safflower oil (controls) or 4% tripalmitin (essential fatty acid (EFA) deficient) both in vivo and in vitro in lung slices. Desaturation, as measured by appearance of 14C-labeled monounsaturated fatty acid in pulmonary total lipid and phospholipids, was significantly greater in vivo and in vitro in lung tissue from EFA-deficient rats. In vitro peincubation of lung slices for 1 to 4 hr with 1 mM oleic, linoleic, or linolenic acid reduced the extent of desaturation of [1-14C]-stearic acid significantly in both dietary groups, but the effect was greater in EFA-deficient tissues. The effect of linoleic acid was always greater than that of oleic acid. Preincubation with palmitic acid and 16,16-dimethyl PGE2 was without effect. Thus: 1) EFA deficiency has been shown to enhance desaturation of palmitic and stearic acid in lung; 2) in vitro addition of linoleic or linolenic acid inhibited desaturation significantly; and 3) oleic acid was inhibitory but to a lesser and more variable extent. Palmitic acid was not inhibitory.

Alterations in phosphatidylcholine species and their reversal in pulmonary surfactant during essential fatty-acid deficiency.

Previous studies (Kyriakides, E.C., Beeler, D.A. and Balint, J.A. (1974) Clin. Res. 22, 717a, and Burnell, J.M. and Balint, J.A. (1975) Fed. Proc. 34, 426) have indicated that essential fatty-acid deficiency in rats resulted in significant reduction of palmitate content of lung tissue and lavage phosphatidylcholines. Experiments were, therefore, undertaken to confirm and further characterize these changes and to examine the reversal of these alterations when essential fatty acid deficient rats were fed fat-free diets supplemented with linoleate for 1-14 days. Analysis of the fatty acid composition of liver lipids was used to confirm the presence of essential fatty-acid deficiency in rats that were fed a fat-free diet supplemented with 4% by weight of tripalmitoylglycerol for 14 weeks. Phosphatidylcholines from lung tissue and lavage fluid of essential fatty-acid deficient rats contained significantly less palmitate and significantly more palmitoleate and oleate than those rats receiving linoleate. These changes in fatty acid composition were reflected in a significant reduction of disaturated phosphatidylcholines (predominantly dipalmitoyl) in lung tissue and lavage fluid from essential fatty-acid deficient rats, while the total phosphatidylcholine content remained unchanged. On feeding the diet containing linoleate to the deficient rats, a reversal of these changes began after one day and was nearly complete by 7-14 days.

Studies of the hepatic excretory defects in essential fatty acid deficiency. Their possible relationship to the genesis of cholesterol gallstones.

Male hamsters were fed normal and essential fatty acid (EFA)-deficient diets for at least 12 wk before bile duct cannulation. With [32P]phosphate, hepatic synthesis of lecithin was similar, but biliary excretion of newly synthesized lecithin was significantly reduced in EFA-deficient compared to that in normal hamsters. Hepatic uptake of intravenously infused taurocholate (TC) and taurochenodeoxycholate (TCDC) were similar in both groups of animals. However, biliary excretion of intravenously infused TC was significantly reduced in EFA-deficient hamsters, whereas that of TCDC-was unchanged. The absolute rate of biliary cholesterol excretion was similar in both groups. Canalicular bile flow, as measured by [14C]erythritol clearance after functional nephrectomy, was significantly lower, with both the bile salt-dependent and independent fractions of this flow being diminished in EFA-deficient hamsters infused with TC. It is concluded that EFA deficiency leads to impaired biliary excretion of taurocholate, lecithin, and water, while cholesterol transport is unaffected, and thus results in supersaturation of bile with respect to cholesterol and production of lithogenic bile.

Studies in the biosynthesis of hepatic and biliary lecithins.

Male rats with biliary cannulae were injected with linoleate-1-(14)C, stearate-1-(14)C, palmitate-9-10-(3)H, phosphate-(32)P, l-methionine-methyl-(14)C, and choline-methyl-(3)H in various combinations and the incorporation of these isotopes into the phospholipids of liver, bile, and plasma was determined for 1-4 hr. The results summarized below favor the view (a) that exchange of saturated fatty acids plays a role in the formation of lecithins; (b) that the unsaturated fatty acids do not undergo significant exchange and determine the pathway of biosynthesis of lecithins; and (c) that there is either more than one pool of CDP-choline in liver or a pathway of biosynthesis of lecithin from choline not involving CDP-choline as an intermediate. Linoleoyl lecithin of liver attained higher specific activity with respect to phosphate-(32)P and choline-methyl-(3)H than did arachidonoyl lecithin. Lecithin in bile attained higher specific activities with respect to phosphate-(32)P, choline-methyl-(3)H, and linoleate-1-(14)C than the corresponding hepatic lecithins. Stearate-1-(14)C and palmitate-9-10-(3)H attained highest specific activities in the hepatic lecithin fraction rich in arachidonic acid. The specific activity of hepatic phosphatidyl ethanolamine was lower with respect to saturated fatty acids, but much higher with respect to (32)P than any lecithin. The ratio of specific activity of (3)H in methyl groups from choline to (14)C in methyl groups from methionine in hepatic sphingomyelin was lower than in hepatic linoleoyl lecithin.