Effects of correction of hypocalcemia on cardiac function in the newborn lamb.

The effect of correction of hypocalcemia on cardiac function in the neonate is unclear. Therefore, we evaluated changes in hemodynamic variables and cardiac contractility in a hypocalcemic neonatal lamb model. Baseline serum ionized hypocalcemia was induced via chelation with intravenous EGTA. Cardiac contractility, measured as end-systolic elastance, did not change with correction of hypocalcemia in this model. In contrast, the variable dP/dt(max), a load-dependent index of contractility, showed an increase with calcium administration while the end-diastolic volume decreased, suggesting that diastolic function or early systolic function had changed. Systemic vascular resistance, cardiac output, and heart rate did not change significantly with correction of hypocalcemia. The results of this study suggest that in our newborn lamb model, cardiac contractility is insensitive to ionized calcium and may reflect cardiac immaturity, but that there may be an effect of calcium administration on diastolic or early systolic function.

Transplacental passage of iohexol.

We describe the appearance of an iodinated, low molecular weight radiographic contrast agent, iohexol, in the intestines of twin neonates after administration to a pregnant mother during angiography. Nonionic contrast agents cross the human placenta and enter the fetus in significant concentrations and in this case facilitated identification of an omphalomesenteric duct cyst in one twin.

Bisdiamine inhibits extracellular matrix formation and cell proliferation of atrioventricular mesenchyme from developing chick heart valves.

Abnormalities of the cushion tissues lead to atrioventricular septal defects (AVSD) and truncus arteriosus (TA). Bisdiamine exposure in the embryo frequently causes AVSD and TA in the newborn chick, mouse, or rat. We studied the effects of bisdiamine on mesenchymal cells grown in aggregate culture isolated from the developing atrioventricular valves of the stage-36 chick embryo. Fibronectin extracellular matrix formation and cell proliferation in the aggregates were assessed in various media. Chick serum stimulated the cells to produce an extracellular matrix and to divide, and the inclusion of bisdiamine inhibited both responses. If we isolated an extracellular matrix from a monolayer of mesenchymal cells and added the sonicated matrix to the medium containing serum and bisdiamine, the matrix incorporated into the aggregates and the cells entered the mitotic cycle. Our previous work established that cells need to attach to an intact extracellular matrix to begin cell division. Thus, we suggest that bisdiamine inhibits the normal formation of the extracellular matrix, leading to reduced cell proliferation, but it does not affect matrix-cell interaction. The lack of cushion growth in situ may be the cause of AVSD or TA.