Conversion Of Linoleate Research Articles

Attenuation of Mammary Duct Development by Menhaden Oil in BALB/c Mice

The predominant polyunsaturated fatty acids of the n-6 family found in corn oil (CO) are crucial for normal mammary duct formation when fed to animals. However, as shown here, not all polyunsaturated fatty acids are equally effective in stimulating mammary gland development. The n-3 fatty acids in a 10% menhaden oil (MO) diet fed to mice effectively reduced both the diameter and the length of the growing mammary ducts. Previously, we demonstrated a similar reduction in duct growth by feeding a 10% fat diet high in those saturated fats found in hydrogenated cotton seed oil. The inhibited rate of duct maturation caused by hydrogenated cotton seed oil was reversed when the mice were allowed to mature on a diet containing n-6 fatty acids prior to feeding the saturated fat diet. The addition of 1% CO to a 9% hydrogenated cotton seed oil diet fed to immature mice was also sufficient to restore duct growth. Mice fed menhaden oil diets, on the other hand, continued to show impaired ductal growth well into adulthood. Examination of the ovaries from MO-fed mice as compared with CO-fed mice revealed significantly fewer corpora lutea. When exogenous progesterone was given to MO-fed mice, ductal growth was partially restored, but not to the extent seen in mice fed corn oil diets. Investigation of the fatty acid contents of livers of these mice revealed reduced amounts of arachidonate (20:4) in MO-fed mice when compared with CO-fed animals. The addition of 1% CO to the 9% MO diets did not alter the arachidonate content, indicating a block in the conversion of linoleate (18:2) to 20:4 by the n-3 fatty acids. Hence, dietary n-6 fatty acids are essential for normal mammary ductal development when fed prior to maturation. Although saturated rats are ineffective, n-3 fatty acids can partially substitute for the required n-6 fatty acids in both ductal and ovarian development.

Fatty acid desaturation and microsomal lipid fatty acid composition in experimental hypothyroidism.

We have studied the influence of experimental hypothyroidism in the rat on the synthesis of unsaturated fatty acids and on liver microsomal lipid fatty acid composition. Hypothyroid rats demonstrated an 80% decrease in delta 9 (stearate) desaturation and a 43% decrease in delta 6 (linoleate) desaturation. Liver microsomal fatty acid composition was altered in the hypothyroid animals with a significantly decreased proportion of arachidonate and increased proportions of linoleate, eicosa-8,11,14-trienoate, eicosapentaenoate and docosahexaenoate. The bulk of these changes occurred in both of the two major phospholipid components, phosphatidylcholine and phosphatidylethanolamine. All of the changes were corrected by treatment of the hypothyroid rat with 25 micrograms of tri-iodothyronine/100 g body wt. twice daily. The diminished delta 9 desaturation did not lead to any changes in fatty acid composition. The increased linoleate and decreased arachidonate levels may be due to the diminished delta 6 desaturase activity, the rate-controlling step in the conversion of linoleate into arachidonate. The increases in the proportions of the other polyunsaturated fatty acid components cannot be explained by changes in the synthesis of unsaturated fatty acids, but are probably due to diminished utilization of these fatty acids.

Incorporation and metabolism of fatty acids by cultured dissociated cells from rat cerebrum.

AbstractDissociated brain cells in culture incorporate a variety of saturated and unsaturated fatty acids into their cellular lipids. Of the various fatty acids studied, uptake of radioactivity was greatest for stearic acid and decreased progressively with decreasing chain length. Incorporation of radioactivity from linoliec and linolenic acids was more extensive than from oleic acid. Cellular phospholipids and triacylglycerols were labeled preferentially from all fatty acid precursors, with the relative amount of label in phospholipids being greatest when cells were incubated with linolenic acid. Fatty acids underwent desaturation and chain elongation. Changes in the labeling pattern of phospholipid fatty acids in the course of incubation demonstrated precursor‐product relationships for laurate (12∶0), myristate (14∶0), palmitate (16∶0), and stearate (18∶0) and for linolenate (18∶3), eicosapentaenoate (20∶5), docosapentaenoate (22∶5), and docosahexaenoate (22∶6). The appearance of label in 22∶5 and 22∶6 paralleled the entrance of label into the ethanolamine phosphoglyceride fraction. Conversion of linoleate (18∶2 ω6) to arachidonate (20∶4 ω6) could be demonstrated but did not proceed via 18∶3 ω6.