Intrinsic tone and passive mechanics of isolated renal arteries from virgin and late-pregnant rats

The purpose of this study was to investigate whether there are alterations in the intrinsic properties of renal interlobar arteries during pregnancy. Renal interlobar arteries (internal diameter similar to 250 mu m) from virgin and late-pregnant rats wore mounted in a pressurized arteriograph system. Intrinsic tone was quantified as the percent difference in luminal diameter of each artery in the presence of physiological saline solution and while pharmacologically relaxed with papaverine. At pressures between 75 and 125 mmHg, tone was 35-50% less in arteries from pregnant rats (P < 0.05). Endothelial removal reduced tone in arteries from virgin rats but had no effect on arteries hom pregnant rats. Analysis of stress-strain curves (rate constants: pregnant, 6.31 +/- 0.38; virgin, 7.81 +/- 0.78; P < 0.05) indicate that there is a decrease in arterial stiffness in gestation. Thus pregnancy is associated with a reduced intrinsic tone, possibly because of a reduction in an endothelial constrictor influence an the vascular smooth muscle in isolated rat renal interlobar arteries. This effect, coupled with the decreased arterial stiffness, demonstrates the significant arterial adaptation occurring during pregnancy.