Histological similarity of primo vascular systems derived from three internal organs of rats

BACKGROUND The primo vascular system has been suggested as the third circulatory system. Although primo tissues have been observed in various tissues isolated from a number of animal species, including mice, rats, and rabbits, very few reports on the histological characteristics of primo tissues from different body parts are available. This study was designed to compare the histological characteristics of primo tissues isolated from different body parts of rats. METHODS Rats were anesthetized and operated on, to locate primo tissues. The primo tissues were searched at the all organs' surface and in lymphatic vessels using suitable finding methods. The tissues found were then separated and observed by histological test methods. RESULTS This histological study revealed that there was no difference between the histological characteristics of the organ-surface primo tissues, the primo tissues inside lymphatic vessels, and the primo tissues on the falciform ligament. Moreover, primo tissues could be differentiated from those with a similar structure, such as lymphatic vessels and blood vessels, by immunostaining against a-LYVE-1 and a-CD31, and can be observed by specific immunostaining against the Von Willebrand factor (vWF). CONCLUSION The results of this study support the fact that primo tissues could possibly constitute a third circulatory system in the whole-body network.