It has been recognized that a percentage of clone calves suffer from persistent pulmonary hypertension of the neonate (PPHN). It has been proposed by some investigators that an imbalance between vasoconstrictors, such as endothelin (ET-1) and vasodilators (such as NO) are involved in the genesis of the problem. Additionally, some clone calves and human infants are refractory to more traditional therapy or require prolonged treatment for PPHN and these patients appear to have increased smooth muscle in their pulmonary small resistance vessels suggesting chronicity. ET-1 is a known mitogen of vascular smooth muscle.

The purpose of this investigation was to evaluate ET-1 concentrations in the blood of clone, the blood of their surrogate dams and in fetal fluids to investigate the utility of using these fluids for prepartum evaluation of the clone. Blood was collected from calves and their surrogates at the time of delivery into heparin tubes; the plasma was separated by centrifugation and frozen until assayed. Fetal fluid samples were also obtained and frozen. Endothelin-1 concentration was determined using a commercially available RIA. Oxygen-dependent calves were those calves requiring, at a minimum, intranasal oxygen insufflation at rates of 5 or more L/min to maintain SPO2 values of >90%.

Samples were obtained from a total of 40 calves; 13 calves were considered to be oxygen dependent and 27 calves were deemed non-oxygen dependent. Plasma ET-1 concentrations tended to be larger in oxygen-dependent calves (2-sample T test; p=0.16). Fetal fluid ET-1 concentration was significantly larger in the oxygen-dependent group (2-sample T test; p=0.0003). No difference between groups was detected in ET-1 measured in the blood of the surrogates; however, maternal blood ET-1 concentration was weakly but significantly correlated with fetal fluid ET-1 concentration overall (Correlation=0.456; p=0.007) and the correlation was stronger within the oxygen dependent group (Correlation 0.780; p=0.002). These data suggest that ET-1 may play a role in pulmonary function abnormalities in clone calves in the immediate post-partum period.