Kinetics of the incorporation of dietary fatty acids into serum cholesteryl esters, erythrocyte membranes, and adipose tissue: an 18-month controlled study.

Tissue levels of n-3 fatty acids reflect dietary intake, but quantitative data about rate of incorporation and levels as a function of intake are scarce. We fed 58 men 0, 3, 6, or 9 g/d of fish oil for 12 months and monitored fatty acids in serum cholesteryl esters, erythrocytes, and subcutaneous fat during and after supplementation. Eicosapentaenoic acid (EPA) in cholesteryl esters plateaued after 4-8 weeks; the incorporation half-life was 4.8 days. Steady-state levels increased by 3.9 +/- 0.3 mass % points (+/- SE) for each extra gram of EPA eaten per day. Incorporation of docosahexaenoic acid (DHA) was erratic; plateau values were 1.1 +/- 0.1 mass % higher for every g/d ingested. Incorporation of EPA into erythrocyte membranes showed a half-life of 28 days; a steady state was reached after 180 days. Each g/d increased levels by 2.1 +/- 0.1 mass %. C22:5n-3 levels increased markedly. Changes in DHA were erratic and smaller. EPA levels in adipose tissue rose also; the change after 6 months was 67% of that after 12 months in gluteal and 75% in abdominal fat. After 12 months each gram per day caused an 0.11 +/- 0.01 mass % rise in gluteal fat for EPA, 0.53 +/- 0.07 for C22:5n-3, and 0.14 +/- 0.03 for DHA. Thus, different (n-3) fatty acids were incorporated with different efficiencies, possibly because of interconversions or different affinities of the enzymatic pathways involved. EPA levels in cholesteryl esters reflect intake over the past week or two, erythrocytes over the past month or two, and adipose tissue over a period of years. These findings may help in assessing the intake of (n-3) fatty acids in epidemiological studies.

Dual anomeric specificity of phosphomannoisomerase assessed by 2D phase sensitive 13C EXSY NMR.

The reversible conversion between D-mannose 6-phosphate and D-fructose 6-phosphate catalyzed by yeast phosphomannoisomerase was studied by phase sensitive 2D 13C-(1H) EXSY NMR spectroscopy at 100.623 MHz, using 13C enriched substrates in the C2 position of the D-hexose 6-phosphates. The unique pair of isomerization cross-peaks observed in the 2D EXSY map correlates the 13C2 resonances of the beta-anomers of both D-[2-13C]-mannose 6-phosphate and D-[213C]-fructose 6-phosphate. This indicates that phosphomannoisomerase specifically catalyzes the reversible conversion between beta-D-mannose 6-phosphate and beta-D-fructose 6-phosphate. Since phosphoglucoisomerase was recently found to catalyze specifically the interconversion of alpha-D-glucose 6-phosphate and beta-D-fructose 6-phosphate, the beta-anomer of the ketohexose ester could be directly channeled in a multi-enzyme system involving phosphoglucoisomerase, phosphomannoisomerase and phosphofructokinase.

Biological markers of dietary intake, with emphasis on fatty acids.

The level of certain polyunsaturated fatty acids in body fluids or tissues can be a valid indicator of their consumption in man. In 59 housewives studied over a 2.5-year period we found a correlation of 0.70 between the intake of linoleic acid, assessed as the mean of nineteen 24-hour recalls, and the level in fat tissue [Van Staveren et al.: Am J Epidemiol 1986; 123:455-465]. In 58 adult men supplemented with fish oil capsules for 1 year, the rise of eicosapentaenoic acid levels in erythrocyte membranes was strongly and specifically related to the rise in intake. We conclude that epidemiological studies of the role of these fatty acids in health and disease could fruitfully employ these markers of dietary intake.

Steroidogenesis during induced oocyte maturation and ovulation in the African catfish,Clarias gariepinus.

Changes in ovarian steroidogenesis accompanying oocyte maturation and ovulation were studied in the African catfish,Clarias gariepinus. Laboratory-reared females with postvitellogenic ovaries were treated with pimozide and LHRH-analogue. The plasma gonadotropin levels were determined by means of a homologous radioimmunoassay, the condition of the ovaries was studied by histological examination of the follicles, and the steroidogenetic capacity of the ovaries was analyzed byin vitro incubation of tissue fragments for 3 h with [(3)H]-pregnenolone and [(3)H]androstenedione as precursors. Data were collected at regular intervals between 0 and 16 h after pimozide-LHRH analogue administration.Until 4 h after the beginning of the experiments the plasma gonadotropin levels did not rise above 25 ng/ml, the ovaries remained in the stage of postvitellogenesis, and testosterone was the main end product of steroidogenesis. Four hours later the gonadotropin concentration in the blood had risen to more than 150 ng/ml, and the ovaries had entered the stage of germinal vesicle migration. At the same time steroidogenesis shifted towards the production of 17α,20ß-dihydroxy-4-pregnen-3-one, 5ß-pregnane-3α, 17α-diol-20-one, 5ß-pregnane-3α,6α,17α-triol-20-one, 5ß-pregnane-3α,17α,20ß-triol and 5ß-pregnane-3α,6α,17α,20ß-tetrol. During the subsequent stage of germinal vesicle breakdown the plasma gonadotropin level remained high, and the synthesis of the C21-steroids showed a further increase. Simultaneously, the production of some C19-steroid glucuronides was enhanced. The preovulation and especially the postovulation stages were accompanied by a gradual decrease in steroidogenic capacity of the ovaries, even though the plasma gonadotropin level remained high. It is concluded that the prematuration surge of gonadotropin influences the activity of enzymes involved in steroidogenesis, leading to a reduced C17,20-lyase and to an augmented activity of the enzymes 20ß-hydroxysteroid dehydrogenase (HSD), 5ß-reductase, 3α-HSD, 6α-hydroxylase and UDP-glucuronosyltransferase. During ovulation the activity of all steroidogenic enzymes, including such key enzymes as 3ß-HSD and 17α-hydroxylase, gradually decreases.Not only 17α,20ß-dihydroxy-4-pregnen-3-one, but also the 5ß-reduced pregnanes may be involved in inducing oocyte maturation and/or ovulation. The very polar triol and tetrol products may function, together with the steroid glucuronides as sex pheromones.

5 beta-pregnane-3 alpha,6 alpha,17 alpha,20 beta-tetrol and 5 beta-pregnane-3 alpha,6 alpha,17 alpha-triol-20-one: steroids of ovarian origin in the African catfish, Clarias gariepinus, during oocyte maturation.

At the stage of oocyte maturation, three very polar steroids were demonstrated by in vitro incubations with tritiated pregnenolone in the ovaries of the African catfish, Clarias gariepinus. Two of these compounds could be identified by chromatography, derivatization, and oxidation as 5 beta-pregnane-3 alpha,6 alpha,17 alpha,20 beta-tetrol and 5 beta-pregnane-3 alpha,6 alpha,-17 alpha-triol-20-one. Blood plasma analysis by means of gas chromatography followed by mass spectrometry confirmed the presence of these steroids with selected ion monitoring. The occurrence of the five most characteristic ions of each steroid was demonstrated at the proper retention times and with the correct abundance ratios. These very polar steroids, which were identified in vitro and in vivo, might have a function in maturation and ovulation induction.