Big endothelin in plasma and amniotic fluid

We previously demonstrated that endothelin-1 (ET-1) exists both in the peripheral circulation and the amniotic fluid (AF). The objects of the present study were (a) to measure the concentrations of ET-1 and big endothelin (big ET) in plasma and AF by radioimmunoassay (RIA) and (b) to characterize the molecular forms of endothelin in human AF by high-performance liquid chromatography (HPLC) coupled with RIAs. Plasma samples from healthy male and female volunteers, and AF samples from full-term and mid-trimester pregnant women were extracted by C₁₈cartridges. Big ET, like ET-1, exists both in plasma and in AF. Significant increases (p < 0.01) of big ET and ET-1 in AF from mid-trimester to full-term pregnancy were observed. The reverse-phase HPLC elution profile of immunoreactive (ir-) ET-1 presented a single major peak at a position corresponding to that of the standard ET-1 in the extracted AF. Two major components of ir-big ET were revealed: One corresponded to the elution position of standard big ET; the other one to that of the standard endothelin fragment [22-38] (EF). In conclusion: (a) Three molecular forms of ET exist in AF; ET-1 as a major form, big ET, and EF, (b) ET-1 and big ET are both present in higher concentrations in AF at full-term pregnancy than during mid-trimester.