DEVELOPMENTAL-CHANGES IN THE ACCUMULATION OF NOREPINEPHRINE AND THE CHRONOTROPIC EFFECTS OF CATECHOLAMINES IN ISOLATED RAT ATRIA AS INFLUENCED BY DIETARY-LIPID

Abstract

Pregnant rats were fed semisynthetic diets enriched in either saturated fat (coconut oil) or polyunsaturated fat (sunflower oil), and sympathetic function was observed in the resulting neonatal pups. The neuronal accumulation of [3H]norepinephrine was significantly decreased in atria from neonates (11, 24 and 37 days of age) of dams receiving dietary sunflower oil compared with the coconut oil diet. The nonspecific accumulation of [3H]norepinephrine occurring in the presence of desipramine (5 .times. 10-5 M) was not changed by dietary lipid treatment. No differences in the accumulation of [3H]norepinephrine were observed in atria from day 7 neonates or in atria from adults which had received the diets since birth. When the beating rate of isolated atria was studied upon exposure to norepinephrine and isoproterenol, it was observed that the EC50 for these agonists was not changed upon exposure to the diets but that the maximal effect of both agonists was increased in atria from adult animals fed coconut oil relative to the sunflower oil diet. No significant differences were observed in the chronotropic effects of either norepinephrine or isoproterenol in atria from 11 day old rats. A developmental analysis of the chronotropic response of isolated atria to a maximally effective dose of norepinephrine (10 .mu.M) revealed a gradual onset of the altered maximum effects found in adult rat atria. Sympathetic nerve regulation of myocardial function can be modified during development by changing the dietary fat composition. The results are discussed in reference to the perturbation of specific membrane-associated processes that may be brought about by dietary lipid treatment and the possible importance of each of these effects in the changes observed in the accumulation of norepinephrine and the chronotropic effects of catecholamines in isolated rat atria.