Long-term effect of dietary alpha-linolenic (ALA) or docosahexahenoic (DHA) acid on the incorporation of DHA in membranes and its influence on the cardiac function in rats in vivo

The present study was designed to evaluate if a high (20% of the fatty acids) and long term intake of dietary ALA as supplied in the diet as whole grain extruded linseed (Valorex SA) can increase the endogenous production of the long-chain n-3 PUFAs in healthy adult rats, and influence heart rate and adrenergic response as well as a DHA-rich diet. The enrichment in DHA was evaluated using fatty acid analysis by GC in various membranes (heart, brain,…) after 2, 4, 6 and 8 months of feeding (n=7) from male Wistar rats (Charles River France) randomly assigned to 3 groups (n=36) and fed a normal fat diet (NFD), a ALA-rich diet (ALA) or a DHA-rich diet (DHA). Our results showed that dietary ALA allowed a significant increase of DHA (and DPA) in cerebral and cardiac membranes, and in a lesser extent in other tissues, as compared to NFD fed rats. The ALA-rich diet allowed an enrichment of DHA in heart about 10% of total fatty acids, while with DHA-rich diet it reached 20% as compared to NFD (4%). The fatty acid-induced print was established after a 2-month feeding period in animals and continued in the time course of the experiment, and whatever the diet, DHA decreased with age. Nevertheless a supply of pure DHA maintained this amount over 15%, limit to get its anti-arrythmic effects. Moreover heart from old ALA- fed rats remained richer in DHA than those from young NFD rats. In parallel 3 groups (n=8) were used to determine the heart rate (HR) from ECG recordings in anaesthetized rats still after the same feeding periods (adrenergic stimulation challenge). Our results showed a decrease in basal heart rate with ALA (395±24,9 bpm) even if it was not as wide as those obtained with DHA (375±26,4 vs 407±36,7 bpm for NFD) throughout the experiment. More in details, the cardiac effect of DHA, as expressed as a reduced basal heart rate and an enhanced chronotropic response to adrenergic agonist stimulation, was observed after a two- month feeding period while these effects were obtained also with ALA, but after a delayed period (6 months of feeding). Our results suggested that the regulation of heart rate by nuro- humoral mediators may be controlled by lower content of DHA, such as those brought by a dietary supply of extruded linseed (ALA).