| Abstrakt: |
Extract: This study was designed to investigate the renin-angiotensin system in the fetal lamb. Simultaneous measurements of plasma renin activity (PRA) were carried out in seven acute fetal-maternal sheep preparations at 91, 100, 104, 112, 124, 142, and 145 days of gestational age, respectively (term 145 days). The mean fetal PRA in this group was 4.87 mμ/ml as compared with 1.58 mμ/ml for the maternal plasma. PRA was also measured simultaneously in three intrauterine nonstressed fetuses. Six days after insertion of catheters, the fetal PRA was 9.0, 9.2, and 8.75 mμ/ml, respectively, and the maternal PRA was 0.4, 4.5, and 3.75 mμ/ml, respectively.The fetal response to aortic constriction was studied in three fetuses and the PRA increased from control values of 4.8, 5.5, and 22.2 mμ/ml to 8.0, 11.5, and 34.5 mμ/ml, respectively, within 15 min after initiation of the aortic constriction and continued to rise to maximum levels of 11.8, 25.5, and 38.0 mμ/ml, respectively. PRA then decreased after release to near control levels. The maternal PRA did not change significantly during the study period. PRA was also measured in the in utero fetus after decreasing the blood volume 8–10% by acute controlled bleeding, and the PRA rose from control values of 6.0 and 4.2 mμ/ml to 40.0 and 54.4 mμ/ml within 15 min after blood loss, followed by a return towards control values over the subsequent 30 min.Morphologic studies in five fetuses, 91–141 days of gestational age, indicate that the juxtaglomerular apparatus contains Bowie-positive smooth muscle granular cells and appears well developed in the fetal kidney by light and electronmicroscopy.These studies, therefore, indicate that the renin-angiotensin system is present during fetal development in the sheep and also demonstrate that the fetus does respond to stimuli which, in the adult, result in renin release. However, further studies will be necessary in order to establish a definitive physiologic role for renin in the fetus.Speculation: The renin-angiotensin system appears to be well developed during fetal development. These observations suggest that the enhanced activity of the renin-angiotensin system may play a role in the control of renal hemodynamics and fluid and electrolyte homeostases in the developing fetus. |
