Fate of labeled albumin and erythrocytes following injection into amniotic cavity of sheep

We have previously described a method to measure the amniotic fluid (AF) volume and fetal swallowing rate in near-term sheep by use of 125I-labeled albumin (RISA) and 51Cr-labeled red blood cells (51Cr-RBC). However, when we measured these volumes on consecutive days, reentry of the radionuclides into the amniotic cavity from fetal urine affected the calculated values of AF volume and swallowing rates. In an attempt to clarify the recirculation problem, we injected RISA and Cr-RBC daily for 9 days into the AF of five chronically catheterized pregnant sheep (124 days gestation on the 1st experimental day). We calculated AF volume and fetal swallowing rate, comparing those values to the values corrected for fetal urine isotopic counts. The mean AF volume and fetal swallowing rate measured by RISA were 808 +/- 48 ml (mean +/- SE) and 559 +/- 29 ml/day, respectively. These values were only slightly different from the corrected volumes, 808 +/- 48 ml and 561 +/- 29 ml/day, respectively, because fetal urine 125I activity reached only 4.8% of AF activity even on the 9th day. In contrast, 51Cr-activity in fetal urine on the 9th day showed 47% of the activity of AF. The mean uncorrected AF volume (785 +/- 44 ml) and swallowing rate (561 +/- 31 ml/day) measured by Cr-RBC were different from the corrected values (790 ml and 570 ml/day, respectively). After the 4th day these differences were particularly conspicuous.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet Deposition In Coronary Vasculature During And After Global Myocardial Ischemia

Recent evidence indicates that myocardial ischemia activates circulating platelets. Open heart surgery imposes global ischemia and platelet activation could lead to intravascular platelet deposition in ischemically injured myocardium. Platelets were labeled with111In and 51cr. The radioactive cells were injected into dogs prior to cardiopulmonary bypass. Following bypass the aorta was clamped to induce 60 min of global normothermic ischemia. The clamp was then removed to reperfuse the myocardium. Tissue biopsy 111In and 51cr activity indexed platelet content and the extent of perfusion respectively. The tissue platelet content in excess of that predicted from the tissue blood content was determined. A substantial increase in platelet content (X = 400%) was found during the reperfusion period following ischemic insult. Although platelets were sequestered in other organs the increases were moderate and unrelated to ischemia. Thus, the significant excess of platelets found in myocardium during coronary reperfusion indicates the presence of platelet thrombi. Low output failure, a complication of open heart surgery, may be the result of platelet microthrombi lodged in the small vasculature.

Platelet - Serotonin Dynamics in Animals with Prosthetic Arterial Crafts

In dogs with prosthetic aortic grafts, we have documented chronic changes in circulating platelets (Circulation 58: II-225, 1978). Following placement of grafts, serotonin (5HT) levels decreased from 2.01±0.22 to 1.37±0.17 mg/10 platelets (p < .005). Serotonin levels remained low for up to 6 months after graft placement and returned to normal when platelet survival time (PST) began to normalize. Maximum in vitro uptake of 14C-5HT was depressed after graft placement (89.0±0.71 before vs 72.0±1.11% after, p <.001), but time to achieve maximum uptake was much less (16.5±2.4 before vs 5.0±2.8 sec. after, p <.001). In vivo release of 5HT was assessed by labelling autologous platelets with 51Cr and 14C-5HT. In animals with grafts, PST was shortened but 14C label survived 1.55±0.10 times longer than 14Cr label. This was significantly greater (p <.02) than control animals with, normal PST in whom 14C label survived 1.21±0.05 times longer than 51Cr. The ratio of 14C/51Cr activity over 5 days following infusion of double labelled platelets increased from 3.16±0.52 (day 1) to 5.85±1.18 (day 5), p <. 001. Among controls, this ratio increased only slightly (1.99±0.34 to 2.26±0.42) and was significantly less on days 2 thru 5 than in animals with grafts (p <. 05–.005). Urinary 5HIAA excretion, measured for 2 months before and after graft placement, increased from 2644.9±80.6 to 3091.2±96.4 μg/gm creat./day (p <.001). In these animals, we conclude that platelets interact with the prosthetic surface, release 5HT and recirculate. Reutilization of released 5HT occurs but may be limited by depressed uptake. The net effect is a reduction in platelet 5HT.