Stereology of the myocardium and blood biochemistry in aged rats fed with a cholesterol-rich and canola oil diet (n-3 fatty acid rich).

Abstract

The myocardial changes brought about by canola oil (n-3 fatty acid rich) and hyperlipidic diets were studied in 45 rats. Three groups each consisting of 15 animals was separated into (A) which receiving a normal balanced diet; and in groups (CHO) and (O) the animals receiving hyperlipidic and canola oil diet, respectively. These diets were fed to the animals from 21 days until 15 months old, then a blood analysis was performed, after which they were sacrificed and the hearts taken for light microscopic studies. The total lipids serum was extracted and the low density lipoproteins (LDL-C and VLDL-C) and chylomicron fractions were determined as well as the cholesterol concentration in the high density lipoprotein fraction (HDL-C). The myocardium was composed of myocytes and cardiac interstitium, which is made up of connective tissue and blood vessels. The following stereological parameters were determined: a) from myocyte: volume density of myocyte, total volume of myocytes surface density of myocyte, total surface of myocyte and cross sectional area of myocyte; b) from blood vessels: volume density of blood vessels, total volume of blood vessels, length density of blood vessels, surface density of blood vessels, total surface of blood vessels and cross sectional area of vessels; c) from connective tissue: volume density of connective tissue and total volume of connective tissue. The differences were tested by the analysis of variance and Tukey test. The Mantel-Haenezel test analyzed the survival curve test comparing the different groups. Many stereological parameters had significant differences: cardiac weight, thickness of the right and left ventricular wall, aorta and pulmonary artery inner diameters. HDL-C, LDL-C, volume density of myocyte, total surface of myocyte, surface density of myocyte, total surface of myocyte, total volume of blood vessel, length density of blood vessels, surface density of blood vessels, total surface of blood vessels, volume density of connective tissue, total volume of connective tissue. Differences in survival curves were significant between groups CHO x A and CHO x O (p < 0.05) but not between groups A x O (p = 0.48). For the cardiac weight, the smallest values were found in group O. The aorta and artery pulmonary internal diameters were smaller in group CHO. The HDL-C serum was about 40% greater in group O. The LDL-C serum was more than 80% less in the same group. The average of volume density of myocyte was less in group CHO, while the average of volume density of connective tissue was greater in group CHO in comparison to groups A and O. The length density of blood vessels was greater in group O than in groups A and CHO. The surface density of myocyte and surface density of blood vessels were smaller in group CHO and greater in group A. The total surface of myocyte and total surface of blood vessels were greater in group CHO and smaller in group O. Differences were significant between groups A x CHO. The total volume of myocytes was greater in group A, while the total volume of connective tissue was greater in group CHO. The cross sectional area of myocyte and cross sectional area of vessels were greater in group CHO and smaller in group O suggesting that the canola oil diet (n-3 fatty acid rich) preserves the myocardium more than the standard and cholesterol-rich diets.