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 alterat ions in the intrinsic properties of renal interlobar arteries during p regnancy. 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 dif ference in luminal diameter of each artery in the presence of physiolo gical saline solution and while pharmacologically relaxed with papaver ine. At pressures between 75 and 125 mmHg, tone was 35-50% less in art eries from pregnant rats (P < 0.05). Endothelial removal reduced tone in arteries from virgin rats but had no effect on arteries hom pregnan t 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 associ ated 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 a daptation occurring during pregnancy.