LONGITUDINALLY ORIENTATED SMOOTH-MUSCLE CELLS IN RABBIT ARTERIES

Intima formation in vessels, spontaneous or experimentally induced, is generally characterized by the presence of longitudinally orientated smooth muscle cells (LSMC). During an experiment of neo-intima inducti on in carotid arteries in rabbits, by application of a non-constrictiv e silastic cuff, a study was performed to investigate the presence of LSMC in the systemic and pulmonary circulations, in both elastic and m uscular arteries. Three patterns could be distinguished: intimal cushi ons in muscular arteries, single or small groups of LSMC in the intima in elastic and larger muscular arteries, and intra-medially located l ayers or columns of LSMC in the aorta, the pulmonary artery, at the bi furcation of the aorta and around orifices of branches. In order to un derstand this peculiar orientation a biomechanical approach was used: this showed that near the lumen the circumferential stress is 4.5 time s higher than the longitudinal. Because the cell surface of the smooth muscle cells exposed to this stress per unit vessel length is much le ss in the longitudinal than in the circular direction we conclude that the LSMC align in the direction which allows them to cope most effect ively with the mechanical stresses.