Evidence for hyperplasia in mesenteric resistance vessels of spontaneously hypertensive rats using a three-dimensional disector.

Cellular dimensions in mesenteric resistance vessels from 10 spontaneously hypertensive rats and 10 Wistar-Kyoto rats have been determined using a random volume with an unbiased counting rule as the counting unit (the disector). With this method, vessels first were mounted on a myograph. Media thickness (spontaneously hypertensive rats, 11.3 micron; Wistar-Kyoto rats, 8.6 micron; P less than 0.01), lumen diameter (spontaneously hypertensive rats, 178 micron; Wistar-Kyoto rats, 194 micron; P greater than 0.1), and maximum active wall tension response (spontaneously hypertensive rats, 3.2 N/m; Wistar-Kyoto rats, 2.5 N/m; P less than 0.05) were determined. After fixation, serial sections normal to the long axis of the smooth muscle cells were made. In each vessel, the disector was a defined volume of the vessel wall (volume ca. 25 X 10(3) micron3) which was contained in about eight of these sections. The number of nuclei within the disector was counted using an unbiased, three-dimensional counting rule. On the basis that cells were mononuclear (an assumption that was tested), the ratio of this number divided by disector volume equaled the numerical cellular density. Measurement of the fraction of media taken up by smooth muscle cells then gave mean cell volume (spontaneously hypertensive rats, 563 micron3; Wistar-Kyoto rats, 615 micron3; P greater than 0.1). From the myograph measurements, the number of cells per unit length (spontaneously hypertensive rats, 10.4/micron; Wistar-Kyoto rats, 7.4/micron; P less than 0.05) and maximum force production per cell (spontaneously hypertensive rats, 5.1 microN; Wistar-Kyoto rats, 5.7 microN; P greater than 0.1) could then be calculated.(ABSTRACT TRUNCATED AT 250 WORDS)