Hypertrophy of arteriolar smooth muscle cells in the rat small intestine during maturation.

The purpose of this study was to define structural characteristics for vascular smooth muscle (VSM) cells from the submucosal arteriolar system of the rat small intestine during maturation. Arterioles from 6- to 8-week-old and 10- to 12-week-old male WKY animals were selected from tissue prepared for scanning electron microscopy and mounted on end so that the entire circumference of each vessel could be observed by serial photography using scanning electron microscopy. From each vessel segment, the following measurements were made: outer vessel diameter, number of VSM cells occupying a length of vessel, the number of resolutions each VSM cell makes around the vessel, length of individual VSM cells, and width of lateral processes along their length. At a given age, the length and width of the VSM cell was statistically similar for all types of arterioles. However, the VSM cell increased substantially in length and width from the 6-8- to 10-12-week time periods. The outer diameter for a particular arteriolar type also increased with age. These data suggest that the intestinal vasculature as a common population of smooth muscle cells at a given age in terms of their length, size, and process morphology for the various types of arterioles. Furthermore, maturation of the microvessels is associated with a uniform hypertrophy of the VSM cells from the majority of arterioles such that cells of young adult rats and those of juvenile animals represent distinctly different populations.