THE CAPILLARITY OF THE SUBENDOCARDIUM OF LEFT-VENTRICLE IN RATS REARED AT A LOW-TEMPERATURE FOR MANY GENERATIONS

The cardiac capillarity in adult rats reared at 5 degrees C for 68 gen erations was studied with a double staining method for alkaline phosph atase and dipeptidylpeptidase IV. Capillary density. proportions of ar teriolar, intermediate and venular capillary portions and capillary do main area were measured in the left ventricular wall. Compared with th e control rats which had been brought back from the low temperature al the 12th generation and reared at 25 degrees C since then. the heart and the cardiac cells were hypertrophied. total capillary density incr eased and the capillary domain areas were reduced along the capillary path from the arteriolar to venular capillary portions. The number of the venular capillary portions showed no significant change but the ar teriolar and intermediate capillary portions significantly increased. All these changes suggest that the cardiac capillary network was bette r developed in the cold-reared rats than in control rats. In the cold- adapted rats the hypertrophic changes in cardiac cells are thus accomp anied by improvements in the oxygen delivery capacity. This adaptation provides a basis for the maintenance of increased thermogenesis in ma ny organs. The changes cannot be established by several weeks exposure to low temperature, but only after rats have been bred in a cold room for generations.