ULTRASTRUCTURAL AND MORPHOMETRICAL STUDIES ON THE ENDOTHELIAL-CELLS OF ARTERIES SUPPLYING THE ABDOMINO-INGUINAL MAMMARY-GLAND OF RATS DURING THE REPRODUCTIVE-CYCLE

The ultrastructure of the endothelial cells of the deep circumflex ili ac and caudal superficial epigastric arteries supplying the abdomino-i nguinal mammary gland of female Wistar rats was studied throughout the reproductive cycle with an electron microscope and image analyzer and compared with that of mammary gland capillaries. The subendothelial s pace of the arteries was broader at the virgin and post-weaning stages but narrower in pregnancy and lactation. In some rats, the endothelia l cells of the arteries radiated some blunt processes into the media t hrough fenestrations in the internal elastic lamina. The density of pi nocytotic vesicles (PV) in the arteries (number of PV per mu m(2) of e ndothelial cytoplasm) significantly increased during pregnancy and rea ched its maximum value during lactation, then subsequently decreased d uring the post-weaning stage. The mammary gland capillaries showed the maximum changes of PV during pregnancy and lactation, with twofold an d fourfold increases during the respective periods. The density of mit ochondria increased significantly in the capillaries during pregnancy and lactation. The length of the marginal folds and microvillous proce sses increased significantly during lactation in both the arteries and capillaries, and especially, increased twofold in the mammary gland c apillaries. It is assumed that the ultrastructural changes of the endo thelial cells of the arteries and capillaries are closely associated d uring reproductive cycle with the functional demand of the mammary gla nds.