Internal carotid and vertebral arteries of spontaneously hypertensive and normotensive rats. A morphometric study on extracranial, intraosseous and intracranial arterial segments.

Arteries from spontaneously hypertensive rats (SHR) and Wistar Kyoto controls (WKY) were investigated. Specified cross-sections were collected from the extra- and intracranial parts of the internal carotid arteries, from the carotid segment situated in the skull bone and from intra- and extracranial segments of the vertebral arteries. The internal radius, media thickness and ratio between media thickness and internal radius (m/r ratio) were calculated for a standardized condition implying a smooth and circular internal elastic membrane. The m/r ratio was significantly increased in all arterial segments of 7-month-old SHR compared to WKY. This was caused mainly by decrease of radius in the vertebral arteries and in the intracranial carotid segment. In the extracranial and intraosseous carotid segments the increase of m/r ratio in SHR was mainly due to an increase of media. Whereas the radius was the same in the intra-osseous and intracranial carotid segments of WKY, the m/r ratio was greater intracranially. The results suggest that the physical properties of supporting tissues may influence the normal arterial development and modify the influence of an increased arterial pressure on the vessel wall.