EFFECT OF MODERATE LEVELS OF DIETARY FISH-OIL ON INSULIN-SECRETION AND SENSITIVITY, AND PANCREAS INSULIN CONTENT IN NORMAL RATS

The effect of omega-3 fatty acids derived from fish and marine mammals on subjects with normal glucose tolerance is still unclear. The aim o f the present study was to test whether the hypolipidemia that follows the chronic administration of cod liver oil, rich in polyunsaturated fatty acids (omega-3), to normal rats is accompanied by changes in glu cose metabolism, insulin secretion and sensitivity, and pancreatic ins ulin content. To achieve this goal, male Wistar rats were fed with a s emisynthetic diet (w/w): 62.5% cornstarch, 7% cod liver oil plus 1% co rn oil, and 17% protein (CD + CLO). Control rats were fed with the sam e semisynthetic diet with the only exception that the source of fat wa s 8% (w/w) corn oil (CD). Both diets were administered ad libitum for 1 month. At the end of the experimental period, the results obtained w ere as follows (mean +/- SEM): serum triacylglycerol (mM): CD + CLO 0. 21 +/- 0.04 vs. CD 0.58 +/- 0.05 (p < 0.05); free fatty acids (mu M): CD + CLO 257 +/- 20 vs. CD 288 +/- 22 (p = NS); total cholesterol (mM) : CD + CLO 1.13 +/- 0.09 vs. CD 1.82 +/- 0.06 (p < 0.05); high-density lipoprotein cholesterol (mM): CD + CLO 0.58 +/- 0.08 vs. CD 1.07 +/- 0.04 (p < 0.05); plasma glucose (mM): CD + CLO 6.30 +/- 0.29 vs. CD 6. 28 +/- 0.10 (p = NS); liver triacylglycerol (mu mol/liver): CD + CLO 1 04.1 +/- 11.4 vs. CD 136.8 +/- 4.3 (p < 0.05); glycogen (mu mol/g wet weight): CD + CLO 298.3 +/- 21.0 vs. CD 297.0 +/- 19.0 (p = NS); gluco se-6-phosphate dehydrogenase (U/liver): CD + CLO 37.9 +/- 2.2 vs. CD 5 8.8 +/- 5.0 (p < 0.05); triacylglycerol secretion (nmol/min/100 g body weight): CD + CLO 101.0 +/- 2.0 vs. CD 166.0 +/- 9.7 (p < 0.01); remo val of fat emulsion (K-2% min(-1)): CD + CLO 15.0 x 10(-2) + 0.8 x 10( -2) vs. CD 8.2 x 10(-2) +/- 0.2 x 10(-2) (p < 0.01); intravenous gluco se tolerance (kg 10(-2)): CD + CLO 2.68 +/- 0.37 vs. CD 2.70 +/- 0.14 (p = NS); immunoreactive insulin (mu U/ml/ min): with the area under t he curve between 0 and 30 min CD + CLO 544 +/- 60 vs. CD 1,050 +/- 38 (p < 0.05), with the area under the curve between 0 and 60 min CD + CL O 1,188 +/- 150 vs. CD 2,160 +/- 137 (p < 0.05), and pancreas insulin content (mU/mg pancreas): CD + CLO 1.85 +/- 0.29 vs. CD 2.04 +/- 0.12 (p = NS). In conclusion, the present study shows that the strong hypol ipidemic effect produced by the administration of low doses of fish oi l to normal rats is accompanied by a significant reduction of plasma i nsulin levels without changes in glucose tolerance. Since no changes i n pancreatic insulin content were observed, lower plasma insulin level s, both basal and after an intravenous glucose challenge, may be the r esult of an increased peripheral insulin sensitivity in normoglycemic animals.