抄録
Changes in systolic blood pressure, sodium metabolism and renal function were studied in pregnant Wistar rats (WR) and Spontaneously Hypertensive Rats (SHR) during mating, gestation and 8 weeks postpartum periods. Abrupt reduction in systolic blood pressure, around 27mmHg was observed in SHR during a few days prior to delivery, followed by returning to the previous blood pressure within a week postpartum, whereas no such a phenomenon was taking place in WR. Drinking 1% Nacl solution after weaning induced a lower rate of pregnancy and delivery of SHR, in comparison with WR. Although the systolic blood pressure of SHR was raised beyond 200mmHg during pregnancy, it was decreased by about 40mmHg a day prior to delivery, and subsequently returned to the previous value. Sodium space of SHR was significantly increased at the second (33.8±2.7% BW) and third trimemster (30.7±0.4% BW) in comparison to the pre-pregnacy value (28.0±2.7% BW). In addition, sodium space was significantly lower in the third trimester than that of the second trimester (p<0.001). The result of total exchangeable sodium was similar to that of sodium space (p<0.05). Simultaneous increases in inulin clearance and fractional excretion of sodium in SHR were observed at the thirdd trimester in comparison with pre-pregnancy values (p<0.025, p<0.05). The mechanism of reduction in systolic blood pressure prior to delivery in SHR seems to be compplicated by the following factors: 1) an antipressor substance of placenta, 2) a depressor substance of fetal kidney, 3) an endocrinological change, 4) a hemodynamic change during pregnancy, etc. However, the elevation of glomerular filtration rate and fractional excretion of sodium are believed to play an important role on this mechanism.
