Experimental studies on the endothelium ultrastructure of heart capillaries under moderate (28-30 degrees) and deep (22-24 degrees) hypothermia without perfusion

Ultrastructural changes in endothelial cells (EC) of myocardial capillaries were studied in 24 dogs which underwent hypothermia without perfusion. Bio psy specimens for electron microscopy were taken from the left ventricle of each dog in the control group, during anesthesia (prior to active cooling) , and at the end of moderate (28-30 degrees) and deep (22-24 degrees) artif icial body cooling. The following morphological types of the EC were identi fied both in the control group and in all test groups: those with moderatel y dense cytoplasm, light, dark, and irreversibly damaged cells. Dark cells showed increased numbers of plasmalemmal vesicles and appeared to be more t ransport-specialized as opposed to other types. In all stages of the experi ment the amount of dark cells continuously increased (to 23.80, 34.62, and 47.17%, respectively). On cooling to 28-30 degrees, subcellular manifestati on of reduced synthetic activity of organelles (nucleus; Golgi complex, and rough endoplasmic reticulum) was observed in all types of the EC. These ch anges persisted, or even increased, at the end of deep hypothermia. The tra nsport activity of the EC changed differently in three experimental groups in all cell types. Micropinocytotic activity increased under spontaneous mi ld hypothermia (34-35 degrees) during anesthesia and tended to decrease wit h subsequent artificial lowering of the temperature to 22-24 degrees. These ultrastructural changes seem to make up an integral part of the process of capillary endothelium adaptation to body surface cooling, and they might c ontribute to the development of tolerance to subsequent ischemic exposure d uring cardiac arrest. (C) 1999 Academic Press.