Production of prostaglandins in homogenates of kidney medullae and cortices of spontaneously hypertensive rats fed menhaden oil

Influence of dietary fats upon systolic blood pressure in the rat

Studies were performed to determine whether feeding diets with differing fatty acid content and composition had an influence on systolic blood pressure in the rat. Weanling male rats were fed standard laboratory chow (2.9% fat in total), or synthetic diets (10% fat in total) containing fish oil, butter, coconut oil or corn oil, for 5 weeks. Coconut oil and butter diets were rich in saturated fatty acids, whilst fish oil and corn oil were rich in the n-3 and n-6 unsaturated fatty acids respectively. Systolic blood pressure was measured using an indirect tail-cuff method at the end of the feeding period, and compared to a group of weanling rats. Feeding the different diets did not alter the growth of the rats, so all animals were of similar weights at the time of blood pressure determination. Control (chow fed) animals, at nine weeks of age, had higher systolic blood pressures than the weanling, baseline control group. Fish oil fed rats had similar pressures to the chow fed rats. Corn oil fed rats had significantly lower systolic pressures than the controls. The rats led the diets rich in saturated fatty acids (butter and coconut oil) had significantly higher blood pressures than all other groups. Systolic blood pressure was found to be significantly related to the dietary intakes of saturated and unsaturated fatty acids. The dietary intake of linoleic acid was significantly higher in corn oil fed rats than in other groups. Systolic blood pressure was inversely related to linoleic acid intake. Feeding a diet rich in saturated fatty acids significantly increases blood pressure in the rat. A high intake of n-6 fatty acids, and in particular linoleic acid, appears to have a hypotensive effect. Prenatal exposure of the rats to a maternal low protein diet, abolished the hypertensive effects of the coconut oil diet and the hypotensive effect of the corn oil diet upon young adult females. The intrauterine environment may, therefore, be an important determinant of the effects of these fatty acids on blood pressure in later life.

Alteration of arachidonate levels in tick salivary glands by dietary modification of host blood lipids

Tick saliva contains prostaglandins of the 2-series, believed to facilitate bloodmeal acquisition. Because ticks cannot synthesize the prostaglandin precursor, arachidonic acid, investigations were undertaken to study the uptake, incorporation, and distribution of arachidonic acid in the salivary glands of the lone star tick in vitro and in vivo. Uptake of [3H]arachidonate by isolated salivary glands was reduced in the presence of low concentrations of arachidonic or eicosapentaenoic acids, but much higher, non-physiological concentrations of oleic and linoleic acids were required to inhibit [3H]arachidonate uptake. The incorporation of [3H]arachidonate into triglycerides increased at high concentrations of arachidonic or eicosapentaenoic acid, but not at any concentration of oleic or linoleic acid. Eicosatetraynoic acid greatly inhibited [3H]arachidonic acid. Guinea pigs fed hydrogenated coconut oil, safflower/primrose oil, or fish oil exhibited altered blood lipids; notably increased levels of eicosapentaenoic acid when fed fish oil. Salivary gland lipids in ticks fed on these hosts were also altered. Ticks parasitizing fish oil-fed guinea pigs contained high levels of eicosapentaenoic acid with a 30% reduction in arachidonate levels. The results demonstrated that eicosapentaenoic acid in the host diet had profound effects on arachidonate assimilation by tick salivary glands, which could lead to altered prostaglandin content in tick saliva.

Distribution of plasma phosphatidylcholine molecular species in rabbits fed fish oil is modulated by dietary n-6 fatty acids

The present study examined the distribution of plasma phosphatidylcholine (PC) molecular species in rabbits fed a chow diet supplemented with fish oil (FO) in combination with either hydrogenated coconut oil or the n-6 fatty acid-rich evening primrose oil (EPO) for 4 weeks. Significant proportions of plasma PC molecular species contained long-chain n-3 fatty acids. Addition of EPO to the FO supplemented diet increased the incorporation of n-6 fatty acids into plasma PC molecules; it also raised the proportions of 16:0-18:2, n-6, 18:1-18:2, n-6, 18:2, n-6-18:2, n-6, and 16:0-20:4, n-6. The increase of n-6 fatty acid-containing PC was at the expense of n-3 fatty acid containing PC species. However, feeding n-6 fatty acids did not affect the distribution of PC molecular species based on total carbon chain length. The most interesting observation was that dietary suplementation with EPO, raised the ratio of 22:6, n-3-containing to 20:5, n-3-containing molecular species, suggesting an enhanced conversion of 20:5, n-3 to 22:6, n-3.

Changes in ether-linked phospholipids in rat kidney by dietary alpha-linolenic acid in vivo

We investigated the effects of perilla oil containing a high level of alpha-linolenic acid on in vivo phospholipid metabolism, particularly three subclasses of choline glycerophospholipids (CGP) and ethanolamine glycerophospholipids (EGP), in rat kidney. After three weeks of feeding, a significantly lower proportion (by 35%) of the alkylacyl subclass of CGP was found in the perilla oil, as compared to corn oil-fed animals. The alkylacyl species of EGP was also higher in the perilla oil than in the corn oil-fed animals. These alterations were accompanied by a remarkably lower proportion of arachidonic acid and a higher level of eicosapentaenoic acid (EPA) in all six subclasses of CGP and EGP in the perilla oil-fed animals. The levels of linoleic acid were even higher in the diacyl subclasses of CGP and EGP in the perilla oil group, suggesting that desaturase and elongase enzymes prefer n-3 to n-6 fatty acids as substrates for diacyl species. These data are useful in defining the effects of alpha-linolenic acid on the biosynthesis of renal phospholipids and on the replacement of n-6 with n-3 fatty acids in the six CGP and EGP subclasses.

n-3 fatty acids and renal diseases

There are numerous biologic rationales for the use of n-3 fatty acids in renal diseases, including a possible increase in the renal vasodilatory capacity by a rearrangement of renal prostanoid production, a reduction in the production of proinflammatory leukotrienes, a reduction in the transcapillary escape rate of albumin, and actions limiting cyclosporine-related nephrotoxicity. Studies of animal models of renal disease, mostly of immune-renal disease, support the idea of the possible usefulness of these compounds. The most promising areas of clinical investigation include the reduction of proteinuria in some chronic glomerular diseases, the treatment of immunoglobulin A nephropathy, and the prevention of cyclosporine-induced nephrotoxicity. However, the results of larger clinical studies, some of which are ongoing, are necessary to support the use of n-3 fatty acids in human renal diseases.

Arachidonic acid, prostaglandin E2 and leukotriene C4 levels in gingiva and submandibular salivary glands of rats fed diets containing n-3 fatty acids

The effect of dietary n-3 fatty acids on prostaglandin E2 (PGE2) and leukotriene C4 (LTC4) levels in rat salivary glands and gingiva was examined in two separate nutritional studies. In the first set of experiments, two groups of male weanling Sprague-Dawley rats were fed semipurified diets containing 10% corn oil (control group) or 10% menhaden oil (experimental group). Rats were killed after 8 wk on the diets; the fatty acid composition of total phospholipids and the concentrations of PGE2 and its precursor, arachidonic acid, were measured in gingiva and submandibular salivary glands (SMSG). Dietary n-3 fatty acids were incorporated into the tissue phospholipids. Arachidonic acid levels were reduced by 56% in gingiva and SMSG of rats fed menhaden oil compared with the control rats fed the diet containing corn oil. The concentrations of PGE2 in SMSG and gingiva of rats fed the diet containing menhaden oil were reduced by 74% and 83%, respectively. In a subsequent nutritional study, we tested whether the diet-induced reduction in tissue arachidonic acid levels would also result in a corresponding decrease in LTC4 production. Three groups of rats were fed diets containing 5% corn oil (group 1), 4% ethyl ester concentrate of n-3 fatty acids plus 1% corn oil (group 2), or 5% ethyl ester concentrate of n-3 fatty acids (group 3). After 6 wk of feeding, gingiva and SMSG were analyzed for arachidonic acid content and in vitro production of LTC4.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins and gastric ulcers: from seminal vesicle to misoprostol (Cytotec)

Misoprostol (Cytotec, G.D. Searle & Company, Chicago, IL) is the first of a new class of orally administered prostaglandin analog drugs to be marketed in the United States. Misoprostol was approved for the prevention of gastric mucosal ulcers associated with nonsteroidal anti-inflammatory drugs (NSAIDS) in high-risk patients. This represents a potentially important development in the pharmacotherapy of peptic ulcer disease. The purposes of this article are to review (1) the biochemistry, physiology, and pharmacology of prostaglandins, especially those synthesized by the stomach; (2) the potential role of prostaglandin deficiency in the pathophysiology of gastric ulcer disease; and (3) the role of prostaglandin analogs in the prevention and therapy of gastric ulcer disease and in other conditions. As the mechanism of action of these new drugs differs from that of the histamine H2-receptor antagonists (H2-blockers), prostaglandin analogs will, whenever possible, be compared with the H2-blockers [cimetidine (Tagamet), ranitidine (Zantac), nizatidine (Axid) and famotidine (Pepcid)], currently the cornerstone of peptic ulcer therapy in this country.

Effect of dietary fat on the lipid composition and utilization of short-chain fatty acids by rat colonocytes

The objective of the present studies was to examine the effect of dietary fat on the lipid composition of rat colonocytes and their utilization of short-chain fatty acids (SCFA). Rats were fed 14% beef fat, fish oil or safflower oil plus 2% corn oil in a semi-synthetic base diet for 4 wk. Colonocytes were isolated and their lipid composition was examined. Feeding beef fat and fish oil resulted in an increase in monounsaturated fatty acids and a reduction in omega-6 fatty acids. Feeding fish oil resulted in an enrichment with omega-3 fatty acids. There was no dietary influence on the amount of either cholesterol or phospholipids of colonocytes. Fish oil feeding resulted in significant increase in colonocyte free fatty acids (FFA) as compared to other diets. Dietary fat was found to have no effect on SCFA utilization by colonocytes. Colonocytes were found to utilize SCFA in the order of butyrate greater than or equal to acetate greater than or equal to propionate. The presence of acetate and propionate in the medium had no effect on the rate of butyrate utilization.

Effects of dietary fish oil on biliary phospholipids and prostaglandin synthesis in the cholesterol-fed prairie dog

Cholesterol gallstone formation in the prairie dog is accompanied by an increase in the percentage of biliary phospholipids containing arachidonic acid, and an increase in gallbladder prostaglandin (PG) synthesis, but the pathogenetic significance of these changes is unclear. Dietary supplementation with eicosapentaenoic acid (EPA), an omega-3 fatty acid which is commonly found in fish oil, decreases prostaglandin synthesis in some tissues by replacing arachidonic acid, and by competitively inhibiting prostaglandin synthesis. We studied the effect of dietary fish oil on gallbladder PG synthesis, and the relative abundance of various molecular species of phosphatidylcholines and phosphatidylethanolamines in bile and gallbladder epithelium in the cholesterol-fed prairie dog. Prairie dogs were maintained for 4 weeks on one of four diets: i) control, ii) cholesterol-supplemented (0.34%), iii) menhaden oil (50 g/kg chow), or iv) cholesterol plus menhaden oil. Supplementation with menhaden oil resulted in a replacement of arachidonic and linoleic acids with EPA and docosahexaenoic acids in the phospholipids of bile and gallbladder mucosa. In cholesterol-fed animals, supplementation with menhaden oil prevented increased gallbladder PG synthesis. Menhaden oil also reduced the incidence of cholesterol monohydrate crystals among cholesterol-fed animals (9/20 with cholesterol plus menhaden oil vs 21/22 with cholesterol alone), but the improvement could not clearly be attributed to decreased PG synthesis since supplementation with menhaden oil also increased the total phospholipid concentration in bile, and decreased the degree of cholesterol saturation. These results demonstrate that dietary supplementation with omega-3 fatty acids significantly influences biliary phospholipids, and decreases the incidence of cholesterol monohydrate crystal formation in this animal model.

Effects of dietary n - 3 fatty acids on mass changes and [3H]glycerol incorporation in various glycerolipid classes of rat kidney in vivo

The effects of dietary fish oil containing n - 3 polyunsaturated fatty acids on triacylglycerol synthesis and phospholipid metabolism (including the alkylacyl subclass of choline glycerophospholipids (CGP)) was studied in rat kidney in vivo. After a 3 week feeding period, the triacylglycerol content (in mumol/g kidney) was 47% lower in the fish oil group relative to animals given sunflower oil. This alteration was accompanied by a substantially lower amount of arachidonic acid (20:4(n - 6)) and higher level (mumol/g tissue) of eicosapentaenoic acid (20:5(n - 3)) plus docosahexaenoic acid (22:6(n - 3)) in the triacylglycerol, CGP, and ethanolamine glycerophospholipids (EGP) of the fish oil group. The labelling of triacylglycerol relative to phospholipid from [3H]glycerol following i.p. administration was 49% lower in the fish oil as compared to the sunflower oil group, indicating a suppression of renal triacylglycerol synthesis relative to phospholipid synthesis. Modest differences in the labelling of CGP and EGP were found. A moderate and significantly lower proportional labelling (by 35%) of the alkylacyl subclass of CGP was observed in the fish oil as compared to the sunflower oil animals. These findings may have relevance to eicosanoid and platelet activating factor (PAF) biosyntheses as well as renal function and pathophysiology.

The role of polyunsaturated fatty acids in fish

The physical properties of polyunsaturated and saturated fatty acids are compared in relation to melting points and fluidity. The role of polyunsaturated fatty acids on membrane fluidity and membrane bound enzyme activity is discussed. The influence of the environment, particularly temperature, on poikilothermic animals is considered in relation to membrane fatty acid composition and metabolism. The metabolic role of polyunsaturated fatty acids of the (n-3) series and their interaction with arachidonate metabolism is discussed.

Long term 'marine diet' in Eskimos is not associated with altered urinary excretion of total tetranor prostaglandin metabolites

The total urinary excretion of tetranor prostaglandin metabolites, measured as tetranorprostanedioic acid (TPD), was quantified in traditionally living Greenland Eskimos (E) and compared with that in Caucasian Danes (D). TPD excretion (microgram/24h) was not significantly different between both groups, neither for males (331 +/- 62.4 (E) vs. 331 +/- 25.7 (D), mean +/- SEM, n = 9 and 10) nor for females (190 +/- 31.7 (E) vs. 264 +/- 27.4 (D), n = 11 and 10, P2 greater than 0.05). Since urinary prostaglandin metabolites are thought to reflect the total prostaglandin turnover in vivo, these results suggest that a long-term intake of relatively large amounts of polyunsaturated fatty acids of the (n-3) family does not alter total prostaglandin turnover in vivo. This is in contrast to stimulated prostanoid formation in vitro, and thus suggests a different regulatory role of dietary and tissue fatty acids for 'stimulated' and 'basal' prostaglandin production.

Study of diet and drug interactions on prostanoid metabolism

To study the extent to which combinations of different dietary lipids stimulate or inhibit prostanoid synthesis groups of 12 rats were fed diets containing 10% (w/w) of either safflower oil, hydrogenated coconut oil/safflower oil, cod liver oil/safflower oil or cod liver oil/linseed oil for a period of four weeks. All diets, with the exception of the safflower oil feed, contained similar levels of linoleic acid. Two further groups of rats placed on the cod liver oil diets were injected with indomethacin (4 mg/kg, i.p.) every three days to establish the completeness of dietary prostaglandin (PG) inhibition. In spite of a 20 fold difference in dietary linoleic acid content, the safflower oil group had similar PG generating capacities to the saturated fat control group, suggesting tight metabolic control of PGs and their precursors. Although there were prostanoid variations in tissue responses, both of the cod liver oil diets substantially reduced generation of aortic, whole blood and renal prostanoids, and decreased urinary PG excretion. The degree of inhibition of renal PGs was substantially greater in the cod liver oil/linseed oil group, with prostaglandin levels being 35% lower than those observed in the cod liver oil/safflower oil fed animals suggesting that linolenic acid and the marine oil fatty acids act synergistically to inhibit formation of 2-series prostaglandins. Concurrent administration of omega-3 fatty acids and indomethacin reduced PG levels further than those obtainable by diet alone, demonstrating that the diets did not result in maximal inhibition. Awareness of these various effects is important for both physiological or clinical studies in which dietary manipulations are used as a means of modifying prostanoid synthesis.

Onset of changes in phospholipid fatty acid composition and prostaglandin synthesis following dietary manipulation with n-6 and n-3 fatty acids in the rat

A synthetic diet preparation supplemented with 10% by weight of either safflower oil, hydrogenated coconut oil containing 3% safflower oil, or 'max EPA' fish oil was fed to rats over a 8-week period. Serial measurements of serum fatty acids, serum thromboxane B2 and urinary prostaglandin excretion were taken during the treatment period to assess the rate of change in fatty acid composition and prostaglandin synthesis following dietary manipulation. There was no significant change in weight gain between the dietary groups during the treatment period. Significant changes in serum fatty acids occurred within 48 h of treatment, with the 'max EPA' oil group having arachidonic acid levels reduced by 23% (P less than 0.01) compared to the coconut oil group. Conversely, rats fed safflower oil had an 18% enhancement of arachidonic acid during the same time period. Whole blood synthesis of thromboxane B2 was significantly depressed (P less than 0.01) after 48 h in rats fed 'max EPA' oil compared to the safflower oil or coconut oil groups. This suppression reached a maximum of 65% (P less than 0.001) after 7 days of dietary 'max EPA' oil treatment. The safflower oil and coconut oil-fed groups showed the same levels of serum thromboxane B2 production over the treatment period. Urinary excretion of both 6-ketoprostaglandin F1 alpha and prostaglandin E2 varied significantly (P less than 0.01) between the groups after 7 days of dietary treatment. Rats fed 'max EPA' oil had depressed urinary prostanoid excretion compared to the safflower and coconut oil groups which remained very similar to each other. After the 8-week treatment period rats were killed and the phospholipid fatty acid composition and prostaglandin-generating capacity of platelets, aorta and renal tissue was examined. Prostanoid production by kidney cortex and medulla and segments of aorta was consistently suppressed in rats fed 'max EPA' oil. These observations correlated well with changes in the phospholipid fatty acid profiles in these tissues. This study shows rapid changes in serum fatty acids and thromboxane B2 generation following dietary manipulation, while changes in urinary excretion or prostanoid metabolites occur only after a longer time period.

Dietary modification of fatty acid and prostaglandin synthesis in the rat

Dietary supplements with safflower oil, linseed oil, cod liver oil and hydrogenated coconut oil were given to rats at levels of 5, 20 and 40 energy % to simultaneously assess the effects of both type and level of dietary fat on tissue fatty acid composition and prostanoid synthesis. There was no significant change in weight gain or blood pressure between the dietary groups after the 4-week dietary regimen. The liver oil and linseed oil diets depressed the arachidonic acid content of kidney phospholipids at all levels of supplementation. The arachidonic acid content of plasma lipids was significantly elevated in animals on the safflower oil diet at 20 and 40 energy % while those on the same level of liver oil diet showed a marked reduction in arachidonic acid. Whole blood synthesis of thromboxane B2 varied significantly at all levels of fat supplementation, with the 20 energy % safflower oil fed group showing maximally enhanced thromboxane B2 production compared to the coconut oil group (P less than 0.001). Conversely, the liver oil groups showed depressed thromboxane B2 synthesis at 20 and 40 energy % (P less than 0.01) compared to the coconut oil group and at 5 energy % compared to the safflower oil group (P less than 0.05). Production of 6-ketoprostaglandin F1 alpha and prostaglandin E2 by incubated kidney homogenates only differed significantly between the dietary groups at 40 energy %. Urinary excretion of 6-ketoprostaglandin F1 alpha was increased by 45% and 55% in rats fed the safflower oil diet at 20 and 40 energy %, respectively compared to the saturated fat diet, while in the liver oil groups excretion was reduced by 20% and 32%. Dietary suppression of prostanoid synthesis is explained in part by changes in available arachidonic acid and competitive inhibition of cyclooxygenase by (n - 3) fatty acids. Thus, minor changes in dietary fat can readily alter tissue fatty acid composition, but both the extent and nature of changes in phospholipid and prostanoid metabolism vary markedly according to the tissue site.

Extremely decreased release of prostaglandin E2-like activity from chopped lung of ethyl linolenate-supplemented rats

Three groups of weanling male rats were reared on a fat-free diet for 13 weeks. One group received only the fat-free diet (FF rats), the other 2 groups received the fat-free diet and a daily supplement of 2 energy% ethyl linoleate ([n-6] rats), or 2 energy% ethyl linolenate ([n-3] rats). The chopped lung preparation was used to illustrate an in vitro prostaglandin formation. PGE2-like activity was quantified on rat stomach strip. The release of PGE2-like activity expressed as ng PGE2-equivalent per g lung tissue (mean +/- SD) was 23 +/- 7, less than 6, and 65 +/- 20 for the FF rats, the (n-3) rats, and the (n-6) rats, respectively. PGE2 quantification by radioimmunoassay of the chopped lung effluent collected after passing over the rat stomach strip revealed the same release pattern as the bioassay. Fractionation of chopped lung effluent on HPLC with radioimmunoassay detection indicated that the lung tissue from (n-3) rats released very little PGE3, if any, in spite of a 20:5(n-3)/20:4(n-6) ratio of 5.2 in the lipids of the lung. It is suggested that the pool of arachidonic acid for prostaglandin production in vitro is different from the one which functions in vivo, and the these pools are differently affected by dietary EFA.

Urinary prostaglandin E2 and vasopressin excretion in essential fatty acid-deficient rats: effect of linolenic acid supplementation

Three groups of weanling male rats were fed on a fat-free diet for 13 weeks. One group received only the fat-free diet (FF rats), the other 2 groups received the fat-free diet and a daily supplement of 2 energy% ethyl linoleate ([n-6] rats), or 2 energy% ethyl linolenate ([n-3] rats). Urinary excretion of prostaglandin E2 (PGE2), immunoreactive arginine vasopressin (iAVP), and kallikrein were determined. PGE2 was quantitated with a radioimmunoassay having 4.9% cross-reactivity with prostaglandin E3 (PGE3). After 4 weeks on the diet, water consumption and urinary iAVP excretion increased significantly in the FF rats and the (n-3) rats compared with the (n-6) rats. Urinary PGE2 excretion was the same for all 3 groups during the first 10 weeks; thereafter it decreased in FF rats and (n-3) rats compared with the (n-6) rats. There was no difference in urinary PGE2 excretion between the FF rats and the (n-3) rats, even though large differences were found in the percentage of arachidonic acid (20:4[n-6]), icosapentaenoic acid (20:5[n-3]), and icosatrienoic acid (20:3[n-9]) of total kidney fatty acids as well as of kidney phosphatidylinositol fatty acids. Fractionation of urine extracts on high performance liquid chromatography with radioimmunoassay detection indicated that (n-3) rats excreted very little PGE3, if any. Urine output followed the same pattern, as did urinary PGE2 excretion. Urinary kallikrein was estimated at week 12 only. It was found to be significantly lower in FF rats and (n-3) rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative measurement of prostaglandins E2 and E2 by selected ion monitoring

A method for the simultaneous quantitative analysis of prostaglandin E2 (PGE2) and PGE3 is described. The PG were analyzed by selected ion monitoring as the methyl ester-TMS ether derivatives of PGB2 and PGB3, respectively. The internal standard for the quantification of both species was [3,3,4,4-2H4]PGE2. A linear response over the range 0.6--50 ng (1.7--143 pmoles) was demonstrated for PGE3. The chromatographic conditions used (2% SP-2330 column) afforded nearly baseline separation of the prostaglandins. New standard curves for PGE3 must be developed each time the ion source parameters are changed. In a typical calibration run, the instrumental precision, expressed as coefficient of variation, ranged from 1.1 to 7.2% for PGE2 (3 to 100 ng injected) and from 1.6 to 11.1% for PGE3 (1.5--50 ng injected). The method was applied to the PG analysis of rat renomedullary tissues. The recovery of synthetic PGE2 added to medullary homogenates was 100.5 +/- 1.7% (mean +/- SEM, n = 9), and the recovery of PGE3 was 91.3 +/- 1.4% (n = 9).

Identification and quantification of prostaglandin E3 in renal medullary tissue of three strains of rats fed fish oil

Three strains of rats were fed a fish oil diet to verify their ability to incorporate and convert dietary eicosapentaenoic acid (20:5 omega 3) into trienoic prostaglandins. Our results show that such conversion indeed occurs in kidney medullae homogenates. Specifically, the presence of prostaglandin E3 (PGE3) was established by gas chromatographic-mass spectrometric (GC-MS) analysis. That compound was conclusively identified by comparison of fragment ions and their relative intensities with those obtained from authentic PGE3. Further evidence was provided by studying the recovery of exogenously added PGE3. Further evidence was provided by studying the recovery of exogenously added PGE3. The crude ethyl acetate extracts of the medullary homogenates were methylated and cleaned up by liquid-gel chromatography with Lipidex-5000 prior to conversion to PGB3 for GC-MS analysis. The PGE3 was quantified by selected ion monitoring (SIM) with [3,3,4,4-2H4] PGE2 as internal standard. The levels of PGE3 were similar, about 3 ng/mg of wet tissue, in the 3 strains of rats. Identical in vivo conversion of the 2.0:5 omega 3 fatty acid to PGE3 could not be positively established by analysis of pooled urine specimens.