Free fatty acids in plasma may exert feed-back control of lipoprotein lipase activity.

Free fatty acids released through hydrolysis of triacylglycerols by lipoprotein lipase at the vascular epithelium may act in feedback control of lipoprotein lipase activity.

How does fish oil lower plasma triglycerides?

Studies using dietary fish oil, safflower oil, and palm oil suggest that the decrease in plasma triacylglycerol due to dietary fish oils is somehow related to a decrease in the capacity of the liver to hydrolyze the phosphatidate, which then affects microsomal synthesis of triacylglycerol from diacylglycerol.

The effect of three intravenous fat emulsions containing different concentrations of linoleic and alpha-linolenic acids on the plasma total fatty acid profile of neonates.

We determined the fatty acid profile of total plasma lipids in infants who received one of three intravenous fat emulsions that differed primarily in their linoleic and alpha-linolenic acid content: (I) a safflower oil emulsion, (II) a 50:50 mixture of safflower and soybean oils, or (III) a soybean oil emulsion. After 2 weeks of fat therapy, oleic acid, expressed as a percentage of total plasma lipid fatty acids, decreased in all groups, but less so in group III (p less than 0.01). The linoleic acid percentage increased in all groups, but group I had the greatest increase (p less than 0.05). Group II patients had higher percentages of the linoleic acid metabolites, dihomo-gamma-linolenic acid (II greater than I, p less than 0.05; II greater than III, p less than 0.01) and arachidonic acid (II greater than III, p less than 0.05). Group II patients also had higher levels of alpha-linolenic acid (II greater than I, p less than 0.05) and its metabolite, eicosapentaenoic acid (II greater than I, p less than 0.05). Another alpha-linolenic acid metabolite, docosahexaenoic acid, however, increased in group III, remained stable in group II, and decreased in group I (III and II greater than I, p less than 0.05). We conclude that the content of linoleic acid and alpha-linolenic acid in intravenous fat emulsions results in statistically significant changes in the fatty acid profile of total plasma lipids in infants receiving total parenteral nutrition.

Biosynthesis of [14C]arachidonic acid from [14C]linoleate in primary cultures of rat Sertoli cells.

The conversion of [14C]linoleate to [14C]arachidonate by rat Sertoli cells was established by use of primary cultures. Most of the 14C from [1-14C]linoleate was located in C-3 of the synthesized arachidonate, indicating that the labeled tetraene had originated largely by elongation and desaturation of the intact labeled substrate rather than by mere addition of 14C-acetate generated by bio-oxidation of the radioactive substrate to an already existing 18-carbon precursor. Although a relatively small amount of 14C was present in 18:3 omega 6 and a relatively large amount of 14C was present in 20:2, it was not possible from these data to establish the relative importance of 20:2 in the biosynthesis of arachidonic acid in rat Sertoli cells.

Effect of hypophysectomy and hormone replacement on fatty elongation in isolated microsomes of rat testes.

Effect of hypophysectomy on fatty acid elongation was investigated in isolated rat testicular microsomes incubated with [14C]malonyl CoA. Hypophystectomy resulted in a 40% decrease in total incorporation of 14C into fatty acids of microsomes. Several 18- and 20-carbon fatty acids of testicular microsomes from hypophysectomized rats had less 14C than did those from nonhypophysectomized ones, whereas only docosa-7,10,13,16-tetraenoic acid (22:4w6) had more 14C. Testosterone injected subcutaneously into hypophysectomized rats at a dose of 0.5 mg per day for eight days posthypophysectomy had no apparent effect on either the total 14C incorporated or the distribution of the 14C in the various fatty acids. Daily subcutaneous injections of 50 or 100 micrograms follicle stimulating hormone (FSH) had some effect on both total incorporation and distribution of 14C. Addition of 0.5 mg testosterone to the 50 micrograms FSH gave the same results as the FSH alone. Smaller amounts of stearic acid (18:0) and linoleic acid (18:2) and increased amounts of docosa-4,7,10,13,16-pentaenoic acid (22:5w6) were present in the microsomes of hypophysectomized compared to nonhypophysectomized rats. Testosterone replacement did not affect these differences, but FSH administration was partially effective in altering the values toward those observed in nonhypophysectomized rats. Results obtained in these experiments indicate that there is inhibition of the testicular microsomal fatty acid elongation system in hypophysectomized rats and that, although testosterone is not at all effective in relieving the inhibition, FSH administration is at least partly effective.

The effects of streptozotocin diabetes and of dietary protein content on the composition and metabolism of testicular lipids.

The effect of streptozotocin-induced diabetes on the fatty acid composition and metabolism in testes of rats on diets varying in protein content has been investigated. The protein content of the diet (40, 20, 5%) had little or no effect on essential fatty acid metabolism during the 2 weeks following injection of streptozotocin, but the 5% diet resulted in a high rate of mortality for diabetic rats. Increased amounts of octadeca-9,12-dienoic (linoleic or 18:2) acid and of eicosa-8,11,14-trienoic (dihomo-gamma-linolenic or 20:3) acid and decreased amounts of eicosa-5,8,11,14-tetraenoic (arachidonic or 20:4) acid were observed in testes of some but not all diabetic compared to pair-fed control rats 2 weeks after injection of streptozotocin. Incorporation of 14C from [14C]18:2 into testicular lipids of these rats was determined 26 hr after intratesticular injection. In some rats there was a greater amount of 14C in eicosa-11,14-dienoic acid (dihomolinoleic acid or 20:2) and 20:3 and less 14C in 20:4 of testes of diabetic than in those of control rats. The suggested impairment in conversion of 18:2 to 20:4 was studied further by using [14C]20:3 as the substrate for intratesticular injection. Four hours after administration of the [14C]polyene there was more 14C in 20:3 and less 14C in 20:4 and in docosa-7,10,13,16-tetraenoic (adrenic or 22:4) acid in testes of diabetic than in those of control rats. The results indicate that in diabetic rats at least one enzyme responsible for the decreased conversion of 18:2 to 20:4 is the delta 5-desaturase.

The effects of hypophysectomy and testosterone treatment on the composition and metabolism of testicular lipids.

The effects of hypophysectomy and of testosterone administration on lipid composition and metabolism of rat testicular tissue have been investigated. Increased concentrations of triacylglycerols and cholesterol were observed in testes of hypophysectomized compared to control (non-hypophysectomized) rats on the eighth day posthypophysectomy. Administration of testosterone maintained the concentrations of these lipids at about normal levels. The concentration of phospholipids was not affected by the hypophysectomy. Incorporation of 14C from 1-[14C] linoleate into testicular lipids was determined 24 hours after intratesticular injection. In hypophysectomized compared to control rats there was more 14C in C 16:0, C 20:2 and C 20:3 and less 14C in C 20:4 and C 22:4 of both phospholipids and triacylglycerols. After intratesticular injection of 1-[14C] eicosatrienoate there was more 14C in C 16:0 and C 20:3 and less 14C in C 20:4 and C 22:4 of both phospholipids and triacylglycerols of hypophysectomized compared to control rats. Intratesticular injection of 1-[14C]-arachidonate resulted in less 14C incorporation in C 22:4 in testes of hypophysectomized than in those of control rats. Treatment with testosterone did not affect the metabolism of any of the 14C-substrates. These results indicate that the testicular desaturation of C 20:3 to arachidonate, requiring a delta 5 desaturase, is inhibited by hypophysectomy and that testosterone by itself may control the concentrations of some testicular lipid classes but not the metabolism of the polyenoic acids.

Composition of, and [14C]acetate incorporation into, lipids of rat Sertoli cells in culture.

Primary cultures of rat Sertoli cells were used for the determination of their lipid and fatty acid composition and for a demonstration of their ability to incorporate 14C from [14C]acetate into fatty acids esterified in the cellular lipids. Similar fatty acid compositions were observed in 9-day cultures of Sertoli cells of rats aged 3, 4 or 5 weeks. Cultures of Sertoli cells of 5-week-old rats had relatively less palmitic, linoleic and arachidonic acids and more palmitoleic, stearic, oleic and docosatetraenoic acids than non-cultured cells from the same pool. No difference between these was observed in phospholipid concentration, but the cultured cells had a greater concentration of both total cholesterol and triacylglycerols than did the non-cultured cells. 14C from [14C]acetate added to the culture medium on the 7th (48-h incubation) or 8th (24-h incubation) day was incorporated into fatty acids esterified in cellular lipids. Major incorporation was into phospholipids and triacylglycerols, but cholesterol also was labeled. The fatty acids containing most of the 14C were the saturated fatty acids, oleic acid and docosatetraenoic acid (products of both de novo synthesis and elongation reactions).

Effect of essential fatty acid deficiency on lipids of rat Sertoli and germinal cells.

The effect of essential fatty acid deficiency on lipids of separated rat Sertoli and germinal cells was determined at various time intervals after the animals were placed on a fat-free diet. Alterations in the fatty acid composition typical of essential fatty acid deficiency were noted in the Sertoli cells as well as in germinal cells as early as Days 9-14 on the fat-free diet. These changes included increased concentrations of oleic acid (18:1W9)2 and the appearance of 20:3W9. In some of the rats there were also decreases in linoleic (18:2W6) and arachidonic acids ((20:4W6), but no significant differences were found between Sertoli and germinal cells. Feeding a corn oil diet to rats previously maintained on a fat-free diet for 4 weeks reversed the changes in fatty acid composition of both Sertoli and germinal cells at the times studied. Lipid changes in phospholipids closely reflected those observed in the total lipids. These early changes in Sertoli cell lipids caused by an essential fatty acid deficiency may have important consequences since the Sertoli cell lipids caused by an essential fatty acid deficiency may have important consequences since the Sertoli cells play a significant role in the spermatogenic process.

Toxic activity of purified lipopolysaccharide of Neisseria gonorrhoeae for human fallopian tube mucosa.

An experimental model of human fallopian tubes in organ culture was used to examine the ability of lipopolysaccharide (LPS) of Neisseria gonorrhoeae to damage the fallopian tube mucosa. Gonococcal LPS was purified by hot phenol-water extraction and sequential ultracentrifugation. This LPS was highly lethal for lead-sensitized mice and at a concentration as low as 6 pg/ml reproducibly gelled limulus amoebocyte lysate. Gonococcal LPS damaged fallopian tube mucosa in concentrations as low as 0.015 microgram/ml, a values less than the LPS concentration in organ culture medium surrounding fallopian tube mucosa that was damaged by gonococcal infection. The toxic effect of LPS was neutralized by polymyxin B. Gonococci were shown to elaborate blebs of outer membrane material that is likely to contain LPS. These studies suggest that gonococci elaborate LPS-containing material into their surrounding medium, that the LPS is capable of mediating damage to human fallopian tube mucosa, and that the production of mucosal damage requires the lipid A portion of the LPS molecule.

Lipid composition and gonadotropin-mediated lipid metabolism of the M5480 murine Leydig cell tumor.

The effects of human choriogonadotropin (HCG) stimulation on lipid composition in the murine Leydig cell tumor M5480 grown subcutaneously were determined. The main lipids of the Leydig cell tumor were found to be largely triacylglycerols and phospholipids. Daily in vivo administration of human choriogonadotropin to tumor-bearing mice for 3 days increased the phospholipid content and altered the phospholipid composition of the tumors. There was no demonstrable change in the levels of triacylglycerols, cholesterol, and cholesteryl esters. HCG had no major effect on the fatty acid patterns of the major lipid fractions with the exception of cholesteryl esters, which had a decreased amount of arachidonic acid following HCG-treatment. Results of in vitro incubations of tumor cells prelabeled with [1-14C]arachidonate showed that the label was lost more rapidly from cholesteryl esters of HCG-treated cells than from control cells during (the 12-hour) incubation. Moreover, less [1-14C]acetate was incorporated into the cholesteryl ester fraction of hormone-treated cells than in control cells. HCG stimulated the activity of cholesteryl ester hydrolase in dispersed cells within 3 hours. These results demonstrate that an acute effect of HCG on tumor Leydig cell metabolism is to increase the metabolism of cholesteryl esters, probably by stimulating cholesteryl ester hydrolase activity. The long term effect is an accumulation of phospholipids which may be utilized for membrane synthesis.

The metabolism of polyunsaturated fatty acids in rat Sertoli and germinal cells.

The metabolism of [1-14C] linoleic, [1-14C] arachidonic and [3-14C] docosa-4,7,10,13,16-pentaenoic acids was investigated after intratesticular injection of the labeled compounds and isolation of rat Sertoli and germinal cell. Following injection of either 14C-linoleate or 14C-arachidonate, the specific activity (sp act) of docosa-4,7,10,13,16-pentaenoic acid of Sertoli cells was greater than that of the germinal cells. The data suggest that the Sertoli cells are more active in the biosynthesis of the 22-carbon pentaene than the germinal cells. Differences between these 2 cell types were also noted in the distribution of the incorporated 14C among the various lipid classes. Following intra-testicular injection of 14C-docosapentaenoic acid, a greater proportion of the recovered 14C in Sertoli cells than in germinal cells was present in 20-carton fatty acids, suggesting a greater activity in Sertoli cells in the metabolism of the pentaene. The major portion of the recovered 14C in both cell types was present in triacylglycerols during early time periods and in phospholipids after 24 hr. The possibility of transfer of biosynthesized docosapentaenoic acid from Sertoli to germinal cells is discussed.

Accumulation, nature, and possible functions of the malachite green affinity material in ejaculated human spermatozoa.

An electron microscopic study was conducted on human sperm over an incubation period of 5 to 6 hours in Tyrode's solution at room temperature. Examination of aliquots of the cells, fixed at timed intervals, with glutaraldehyde, malachite green, and postosmication revealed that malachite green affinity material (MGA-M) was barely discernible at first but did accumulate considerably upon standing. Biochemical analysis of MGA-M, which is extractable by glutaraldehyde, revealed that MGA-M is a mixture of extractable phospholipids and of their lyso-derivatives. Some of these substances have fusogenic properties; i.e., they are able to fuse together the membranes of two different cells. The appearance and accumulation of these fusogens occurred during the incubation period of 5 to 6 hours, which was previously shown to be required to capacitate human sperm in vitro. It is probable, therefore, that human sperm, during their initial period of incubation either in vivo or in vitro, not only become capacitated and undergo the acrosome reaction but also develop the fusogenic substance(s) which are necessary for the imminent fusion of their plasma membrane to the vitelline membrane of the mature oocyte.

Desaturation of eicosa-11,14-dienoic acid in human testes.

The metabolism of [1-14C]eicosa-11,14-dienoic acid was investigated in human testes using whole tissue minces and microsomal preparations. Both types of preparations catalyzed the desaturation of the labeled diene to eicosa-8,11,14-trienoic as well as eicosa-5,11,14-trienoic acid. The reported results, therefore, indicate that human testicular tissue, as well as rat testicular tissue (reported previously), is capable of utilizing eicosa-11,14-dienoic acid as a precursor of arachidonic acid. Since it is known that there is no delta 8 desaturase activity in rat liver and brain, these studies support the concept that there is a tissue variation in this enzymatic pathway.

A comparative study of the lipid composition of isolated rat Sertoli and germinal cells.

The lipid composition of enriched preparations of Sertoli cells and of germinal cells, isolated from the testes of mature rats, has been investigated. Sertoli cells contained a much lower content of phospholipids (in particular, much less phosphatidylcholine and phosphatidylethanolamine) and a higher content of triacylglycerols than did germinal cells. In addition, the Sertoli cells had a higher ratio of esterified to unesterified cholesterol than did germinal cells. Total lipids of Sertoli cells contained considerably lower levels of palmitic and docosa-4,7,10,13,16-pentaenoic acids and higher levels of stearic and oleic acid than did the total lipids of germinal cells. The major phospholipid classes and the triacylglycerols of Sertoli cells similarly contained less palmitic and docosa-4,7,10,13,16-pentaenoic acids, more stearic and oleic acids and also more arachidonic acid than did the corresponding lipid classes of the germinal cells. Minor differences between cell types were also noted for the content of palmitoleic, linoleic, docosa-7,10,13,16-tetraenoic, docosa-4,7,10,13,16,19-hexaenoic and tetracosa-9,12,15,18-tetraenoic acids.

The lipid composition of isolated rat spermatids and spermatocytes.

The lipids composition of enriched fractions of spermatids and spermatocytes, isolated from rat testicular tissue, has been investigated. More than 20% of the total fatty acids of spermatids but only 10% of those of spermatocytes, isolated from testes of mature rats, was 4,7,10,13,16-docosapentaenoic acid. Spermatocyte-enriched fractions isolated from testes of immature rats had fatty acid compositions similar to those isolated from testes of mature rats. On the other hand, spermatids isolated from immature rats had a level of docosapentaenoic acid which was intermediate between the level found in spermatocytes and that of spermatids from mature rats. Major phospholipid classes and the triacylglycerols of spermatids contained much more of the docosapentaenoic acid than the corresponding lipid types from spermatocytes. Differences in content of total phospholipids, individual classes of phospholipids and triacylglycerols among spermatocytes, spermatids and late spermatids were also observed.

Metabolism of eicosa-11,14-dienoic acid in rat testes. Evidence for delta8-desaturase activity.

The metabolism of [14C]eicosa-11,14-dienoic acid was investigated in rat testes in vivo and in vitro. Intratesticular injection of [1-14C]eicosa-11,14-dienoic acid resulted in the appearance of radioactivity (4-30% of 14C in total fatty acids) in 20-carbon trienoic fatty acids and a small amount (2-3.5%) in arachidonic acid. Analysis of the 20-carbon trienoic acid fraction by ozonolysis indicated that 15 to 34% of the 14C in this fraction was in an 8-carbon fragment originating from eicosa-8,11,14-trienoic acid. The rest (66 to 84%) was in a 5-carbon fragment, presumably originating from eicosa-5,11,14-trienoic acid. Incubation of testicular tissue minces or microsomes with [1-14C]eicosa-11,14-dienoic acid yielded labeled eicosa-8,11,14- and eicosa-5,11,14-trienoic acids in proportions similar to those obtained in vivo. Added unlabeled acetate had no effect on the formation of [14C]eicose-8,11,14-trienoic acid in vitro. Therefore, it is unlikely that the labeled eicosa-8,11,14-trienoic acid arose from elongation of octadeca-6,9,12-trienoic acid with labeled acetate derived from bio-oxidation of the labeled substrate. These results are compatible with a limited desaturation of eicosa-11,14-dienoic acid to eicosa-8,11,14-trienoic acid and provide evidence for delta8 desaturate activity in rat testis.