Post-weaning heart development and dietary lipid level in the male rat: evolution of lipoprotein lipase activity.
The wet weight evolution and specific and total lipoprotein lipase (LPL) activities of the heart were studied in male rats fed with diets containing 4, 12 or 21 p. 100 lipids from 50 g (3 weeks age) to 400 g body weight (13 weeks of age). The animals were compared at 100, 150, 200 and 400 g. The main results show that:--a lipid-rich diet caused some cardiac hypertrophy beginning at 100 g body weight:--specific LPL activity (activity/g of wet tissue) in the 50-400 g interval was higher when the diet contained more lipids;--when the diet contained 4 p. 100 and 12 p. 100 lipids, specific LPL activity decreased from weaning until a plateau was reached at 200 g body weight. On the other hand, when the diet contained 21 p. 100 lipids, specific LPL activity increased to a maximum in the 150-200 g interval; it then declined rapidly so that at 400 g there were no longer significant differences between the specific LPL cardiac activities of the three groups of animals. The activities thus became independant of the dietary lipid level;--total LPL cardiac activity was higher when the diet contained more lipids, at least up to the 400 g stage. When the diet contained 4 and 12 p. 100 lipids, the activity increased linearly in the 100-400 g interval. When the diet contained 21 p. 100 lipids, it increased very rapidly in the 50-200 g interval then decreased in the 200-400 g interval. In the latter interval, the differences between LPL activities of the three groups were less so that at 400 g there was only significant difference between the extreme high and low lipid groups. Thus, as specific activity, total LPL cardiac activity tended to become independent of dietary lipid level when the animals became adult.