Feasibility of hepatocellular transplantation via the umbilical vein in prenatal and perinatal lambs.

Hepatocellular transplantation has previously been performed in experimental animals by infusion of hepatocyte suspensions into the spleen or portal venous system. Cells injected into these sites flow to the liver and engraft within the hepatic parenchyma. We designed this study to evaluate the feasibility of hepatocellular transplantation through the umbilical vein in the prenatal or perinatal periods. Allogeneic sheep hepatocytes were harvested, stained with the vital fluorescent dye DiI, and injected into the umbilical vein of fetal lambs at 85% gestation and term. Hemodynamic studies performed to assess the physiological impact of transplantation on the recipient animal demonstrated that the procedure was well tolerated. No significant short-term complications were encountered and no lesions were found by conventional histological examination at necropsy 1-17 days after transplantation. Engrafted cells were identified within the liver by fluorescent microscopy and flow cytometry in 4/7 animals constituting 1.2-5% of the hepatocyte population. Fluorescent cellular material with the morphology of hepatocytes, noncellular material, and fluorescent phagocytic cells were seen occasionally in other organs including lung, brain, adrenal, and placenta. These studies demonstrate the feasibility of performing hepatocellular transplantation in the fetus via the umbilical vein in experimental animals.

Thoracic duct lymph flow in fetal sheep with increased venous pressure from electrically induced tachycardia.

The intent of this study was to investigate thoracic duct lymph flow, as it is related to the development of hydrops fetalis during rapid atrial pacing. We studied 6 fetal sheep at 128 +/- 6 days of gestation who had chronically placed thoracic duct catheters, aortic and superior vena cava catheters, and atrial pacing electrodes. Atrial pacing at 317 beats/min caused an elevation in central venous pressure from a baseline value of 3 Torr to 7 Torr without affecting pH, arterial blood gas tensions, aortic blood pressure, total protein concentration, or colloid osmotic pressure, although there was a small rise in hematocrit. The thoracic duct lymph flow rate at baseline was 41 +/- 6 ml/h. After atrial pacing for 6 h, the lymph flow rate as measured over at least three consecutive 10-min intervals, and presumably the transvascular fluid filtration rate, increased to 67 +/- 7 ml/h if it was collected at an outflow pressure of 3 Torr, equal to the venous pressure prior to the onset of atrial pacing. However, if the lymph was collected instead at an outflow pressure of 7 Torr, equal to the actual venous pressure measured with rapid atrial pacing, then the lymph flow rate diminished to 48 +/- 5 ml/h. This difference in lymph flow secondary to the increase in venous pressure could account for a maximum of 19 ml/h of edema that accumulates in fetal interstitium and body cavities with atrial pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of outflow pressure upon thoracic duct lymph flow rate in fetal sheep.

Edema develops when lymph does not return to the venous circulation at a rate equal to the rate of capillary filtration. Fetal sheep develop edema as well as an increased central venous pressure while undergoing atrial pacing at 320 beats per min. We hypothesized that the increased central venous pressure augmented the appearance of fetal edema by impairing the return of thoracic duct lymph to the venous circulation. To investigate this hypothesis, we studied the effect of outflow pressure upon thoracic duct lymph flow in 10 unanesthetized fetal sheep who had low resistance lymph catheters placed in the cervical thoracic duct near its junction with the left jugular vein. After the ewe and fetus recovered for 5 d, we altered the outflow pressure of the lymph catheter by adjusting its height with respect to amniotic fluid pressure and measured the resultant change in thoracic duct lymph flow rate. We found that lymph flow rate was constant over the range of outflow pressures (central venous pressures) normally encountered but decreased in a linear fashion at pressures greater than 0.68 kPa (5.1 torr). Lymph flow stopped at an outflow pressure of 2.40 kPa (18 torr). The data points are best fit by two lines obtained by a piecewise linear regression rather than a single line obtained from a linear regression. We conclude that fetal thoracic duct lymph flow is sensitive to elevations in outflow pressure. Lymph flow begins to diminish at outflow pressures corresponding to central venous pressures commonly encountered in pathologic conditions and may augment the appearance of fetal edema.