Abstract
Awake adult rats were given a solution of [9,10-3H]palmitate ([3H]PAM) by gavage. The appearance of radiolabel in plasma lipid fractions was monitored by thin-layer chromatography at fixed intervals thereafter. At 2 h, the rats were killed by microwave irradiation and radioactivity in whole brain and individual brain phospholipids was determined. In plasma, esterified [3H]PAM was mainly associated with triglyceride, phospholipid, and cholesterol ester. Radioactivity appeared to a larger extent in triglyceride than in unesterified fatty acid, suggesting that unesterified [3H]PAM in plasma was largely due to release from esterified [3H]PAM by lipoprotein lipase hydrolysis. Brain radioactivity could be accounted for entirely by incorporation of unesterified plasma [3H]PAM. Esterified [3H]PAM in chylomicrons or lipoproteins was calculated to make no measurable contribution using a published value for the incorporation coefficient of [3H]PAM into brain in the evaluation. These results suggest that ingested palmitic acid (PAM) in adult rats enters blood as esterified triglyceride within chylomicrons and lipoproteins and, in part, eventually is converted to circulating unesterified PAM. It is the circulating unesterified PAM that is incorporated into brain from blood, whereas esterified PAM within plasma chlomicrons and lipoproteins makes no measurable direct contribution.
Highlights
Awake adult rats were given a solution of [9,10'Hlpalmitate ([3H]palmitic acid (PAM))by gavage
These time courses suggest that the unesterified ['HIPAM was formed mainly by the action of lipases on the ["]PAM esterified within circulating chylomicrons or lipoproteins
Esterified and unesterified forms of ['HIPAM are found in plasma following ingestion of ['HI PAM in adult awake rats, incorporation of ['HIPAM into brain can be explained entirely by uptake of the unesterified radiolabel
Summary
Awake adult rats were given a solution of [9,10'Hlpalmitate ([3H]PAM)by gavage. The appearance of radiolabel in plasma lipid fractions was monitored by thin-layer chromatography at fixed intervals thereafter. Radioactivity appeared to a larger extent in triglyceride than in unesterified fatty acid, suggesting that unesterified ['HIPAM in plasma was largely due to release from esterified ['HIPAM by lipoprotein lipase hydrolysis. Esterified ['HI PAM in chylomicrons or lipoproteins was calculated to make no measurable contribution using a published value for the incorporation coefficient of ['HI PAM into brain in the eva1uation.l These results suggest that ingested palmitic acid (PAM) in adult rats enters blood as esterified triglyceride within chylomicrons and lipoproteins and, in part, eventually is converted to circulating unesterified PAM. It is the Circulating unesterified PAM that is incorporated into brain from blood, whereas esterified PAM within plasma chlomicrons and lipoproteins makes no measurable direct contribution.-Purdon, D., T. No evidence for direct incorporation of esterified palmitic acid from plasma into brain lipids of awake adult rat.
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