Pregnancy-induced changes in resistance blood vessels.

This study was designed to examine the effect of reproductive status on the basic mechanical properties of resistance size blood vessels. The hypothesis to be tested was that pregnancy is associated with alterations in both the passive and active properties of blood vessels small enough to be major determinants of peripheral vasculature resistance. Third-order arteries (165 microns in diameter) from the mesenteric arcade of the rat were removed at all three stages of gestation and the four stages of the estrous cycle. These were placed in a specially designed myograph system in which their active and passive tension-internal circumference characteristics were measured. Pregnancy was found to be associated with a decrease in stiffness of these vessels and a reduction in contractile ability by 20 days' gestation.