Inotropic Response of Rat Heart Papillary Muscle to α 1 ‐and β‐Adrenoceptor Stimulation in Relation to Dietary n‐6 and n‐3 Polyunsaturated Fatty Acids (PUFA) and Age

The effect of dietary n‐6 and n‐3 polyunsaturated fatty acids (PUFA) and age on inotropic responses of heart papillary muscle to α 1 ‐or β‐adrenoceptor stimulation was examined in young (4 months), middle‐aged (12 months) and senescent (27 months) male Wistar rats. From the age of two months the rats were fed a diet containing 2% or 12% of fat by weight varying in PUFA type: a) standard low‐fat n‐6 PUFA diet, b) high‐fat n‐6 PUFA diet or c) high‐fat n‐3 PUFA diet. The inotropic responses to α 1 ‐adrenoceptor stimulation with phenylephrine were triphasic (positive, negative, then positive). Young, high‐fat n‐3 PUFA‐fed rats exhibited significantly lower negative and higher positive responses to phenylephrine stimulation, and higher positive responses to isoprenaline stimulation than young, high‐fat n‐6 PUFA‐fed rats. On the other hand, no such dietary‐related difference was found between young rats fed a high‐fat n‐3 PUFA diet and a standard low‐fat n‐6 PUFA diet. The young high‐fat n‐6 PUFA‐fed rats exhibited inotropic responses similar to those of the middle‐aged and senescent rats within the three dietary groups. The time to peak force and the time of half relaxation did not differ within dietary and age groups. The findings indicate that dietary n‐6 PUFA‐rich supplementation at a young age induces changes resembling the effects of age, as evidenced by decreasing cardiac responses to adrenoceptor agonists, such as phenylephrine or isoprenaline.