Fat accumulation in the rat heart during fasting

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Abstract
Following a short period of fasting, with free access to water, lipid droplet accumulation (LDA) occurs in many glandular organs as well as in the heart of several species. The present work describes the changes in the hearts of male and female rats of different ages (6, 12, 18 and 24 weeks) deprived of food for 1, 2 and 3 days. LDA was demonstrated by staining with Oil Red O and a special “scoring” system was developed based on sections arbitrarily divided into five regions for each ventricle and two for each atrium. Three standard section were studied from each heart. This system largely avoided problems arising from the uneven distribution of fats in different parts of the heart. In control animals very little fat was seen in any part of the heart. The pattern of changes was similar in males and females but the degree of LDA was usually much greater in the male. In both sexes LDA increased after 1 day and usually reached a peak by the second day, followed by a sharp decrease, returning to almost normal. However in both sexes the response in the 18-week-old animals was minimal, with no clear peak. The LDA was always maximal in the R Ventricle, followed by the L ventricle. The heaviest deposition occurred in the superior parts of the ventricles, close to the atria. LDA was comparatively rare in the atria. Fat appeared to be longest in the most heavily loaded regions. Recovery from LDA was rapid, being almost complete 24 hr after returning to a normal diet. Again the most heavily loaded regions retained longest. These findings are discussed in relation ot possible anatomical factors such as the distribution of blood vessels. It It unlikely that such factors offer an adequate explanation and it is suggested that since the uptake of fats into the heart is probably controlled by lipoprotein lipase the distribution of this enzyme in different parts of the heart should be investigated. The histochemical changes are also discussed in relaion to previous biochemical work. Finally it is pointed out that it is common procedure to fast experimental animals overnight and even such a brief period could bring about considerable histological and metabolic changes.