[Reactivity of cortical bone capillaries. Functional TEM analysis with adrenaline, ATP and insulin]

In order to study any morphological effects that vasoactive drugs might exert on cortical bone capillaries, Swiss mice received one intravenous bolus injection each of epinephrine, ATP and insulin. In one control group saline solution was injected and another was not treated. All animals were handled in the same way. A piece of the tibia diaphysis was resected and prepared for transmission electron microscopy (TEM). The lumina and the endothelia of capillaries were submitted to computerized morphometry. Some significant changes were noted: epinephrine increases both the width of the lumen and the endothelium. ATP decreases the endothelium. Insulin (hypoglycaemia?) thickens the endothelium. These finding suggest some physiological hypotheses: the epinephrine-induced widening of the lumen and the thickening of the endothelium might reflect a decreased extravasal space and oedema of cortical bone that might cause the diffusion of minerals to take longer. Intracortical perfusion pressure would then decrease and the bone perfusion rate increase. ATP might reduce the transcapillary diffusion time and increase the extravasal space in cortical bone. Apparently there are specific insulin receptors in cortical bone capillaries.