رسائل ماجيستير
English
2004
Effect of acute and chronic grapefruit, orange and pineapple juice consumption upon blood lipoprotein synthesis and metabolism in the rat
Costantine Daher, Jamil Abou-Khalil
مدرسة الآداب والعلوم-الجامعة اللبنانية الأميركية · لبنان
The effects of acute and chronic juice (grapefruit, orange and pineapple juices) intake on plasma lipid profile and lipoprotein metabolism have been investigated in normolipidemic Sprague Dawely rats. Acute juice intake effects were studied after three hours of a single juice-lipid load instilled intragastric ally. Both pineapple and grapefruit groups had significantly lower plasma and chylomicron (eM) triacylglycerol (TAG) concentrations than the control group. This effect may be attributed to delayed gastric emptying since all juice groups significantly inhibited gastric emptying and resulted in higher intragastric TAG retention 3h postprandially. None of the juice types had an effect on plasma cholesterol. The acute study does not support the possibility of a direct effect of juices on liver during the period studied since very low-density lipoprotein (VLDL) TAG and VLDL cholesterol concentrations of all groups were similar. For a period of six month, animals of the chronic study received either water (control group) or half of their daily liquid intake from one of the following juices: grapefruit, orange or pineapple juice. Blood samples from the different groups were collected following 18 h of fast and subjected to different analyses. Results have shown that when compared with the control group none of the juice types used had a significant effect on blood glucose, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol and the ratios total cholesterol/HDL-cholesterol and LDL-cholesterol/HDL-cholesterol. Only animals of the grapefruit group showed a drastic decrease in plasma TAG concentrations with respect to all other groups. This decrease in mean plasma TAG concentration appeared to be the result of a direct effect of grapefruit juice on liver TAG secretion since VLDL particles of the grapefruit group carried by far the least amount of TAG. Unlike grapefruit group, both pineapple and orange groups significantly increased VLDL TAG secretion with respect to control and grapefruits groups, indicating different impacts of juice types on liver TAG secretion. LDL TAG concentrations of all groups were similar. A significant increase in plasma VLDL apolipoprotein B (apo B) concentration, hence VLDL secretion, has been observed irrespective of the juice type. However, plasma total apo B concentration of the grapefruit group was the highest among all groups, while both orange and pineapple groups had the lowest plasma total apo B concentrations, indicating that either pineapple or orange juice consumption, but not grapefruit, increase the rate of metabolism of lipoprotein particles from the blood. The reduced metabolism and clearance of VLDL particles observed in the grapefruit group may be attributed to the large number and small sized VLDL particles secreted in this group. In conclusion a six-month period of chronic juice intake in normolipidemic rat showed a modest effect on blood lipid profile, and the possible cardioprotective benefit may be through mechanisms independent of a direct effect on blood lipid levels. Orange and pineapple juices but not grapefruit appeared to increase somehow the metabolism and clearance of the lipoprotein particles from the blood. In the acute study, mainly grapefruit and pineapple juices moderate sharp increases in postprandial plasma TAG concentrations accompanying peak digestion and absorption as a result of delayed gastric emptying.
