Abstract
Studies altering plasma calcium levels have demonstrated that the maternal (M) and fetal (F) parathyroid glands appear to function automonously and suggest a lack of placental permeability to PTH. To determine whether the ovine placenta is permeable to PTH I-125, catheters were placed into the F abdominal aorta and pedal vein and M abdominal aorta and jugular vein in 5 date bred ewes at 121 to 135 days gestation. The studies were conducted 24 to 48 hours after surgery when the M and F arterial blood gases and pH returned to normal. Purified intact bovine PTH (1-84) was iodinated by the chloramine-T method. The placenta transfer of tracer quantities of PTH I-125 was studied in 5 animals in the M→F and 4 in the F→M direction. Simultaneous serial F and M plasma samples were obtained during the 60 minute study period and precipitated with 15% trichloracetic acid and the results expressed as percent dose/liter plasma. During the initial 20 minutes of the study, the t 1/2 was 21 minutes (r= -0.99) in the F and 21 minutes in the M (r=-0.99). In the M→F studies, no more than 0.3% of the injection dose/liter plasma was detected in the F and in the F→M studies, no more than 0.5% of the injected dose/liter plasma was detected in the M at 15 to 30 minutes post injection. Thus, during the 3rd trimester, the ovine placenta is impermeable to PTH I-125. The t 1/2 of PTH I-125 is similar in both the ovine F and M.
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Erenberg, A., Weinstein, M., Chen, IW. et al. 182 PLACENTAL IMPERMEABILITY TO PARATHORMONE (PTH) 1–125 IN THE EWE. Pediatr Res 12 (Suppl 4), 394 (1978). https://doi.org/10.1203/00006450-197804001-00187
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DOI: https://doi.org/10.1203/00006450-197804001-00187