Relaxin and progesterone during pregnancy and the post-partum period in association with live and stillborn calves in bottlenose dolphins (Tursiops truncatus)

Abstract

The objectives of this study were to validate a relaxin and progesterone RIA for use in bottlenose dolphins, and quantify and characterize both hormones in extracts of placental tissue and serum collected during pregnancy and the post-partum period, and compare the results between dolphins with live and stillborn calves. In Experiment 1, validation of a heterologous relaxin and progesterone RIA involved specific displacement of antibody-bound radiolabeled human relaxin or progesterone in response to increasing volumes of pooled pregnant dolphin serum and amounts of respective hormone standards added to a fixed volume of serum. The displacement curves were considered parallel and additive relative to respective standard curves. In Experiment 2, immunoreactive relaxin and progesterone were detected in placental extracts and, in corresponding serum samples, concentrations of both hormones were higher during the pre-partum than post-partum periods. Circulatory concentrations of progesterone decreased (P<0.05) from relatively high concentrations during early and mid-pregnancy to intermediate concentrations by late pregnancy (month effect, P<0.0001) in dolphins with live births, whereas, in dolphins with stillbirths, the decrease in progesterone began earlier (month-by-birth status interaction, P<0.007); mean concentrations were lower at mid- (37%, P<0.06) and late (25%) pregnancy. Temporally, relaxin increased (P<0.05) progressively from relatively low concentrations during early pregnancy to high concentrations during late pregnancy (month effect, P<0.0001) and was not different between birth statuses (birth status effect, P=0.76; month-by-birth status interaction, P=0.17). Even though the interaction did not reach significance, mean relaxin concentrations were 42%, 29%, and 34% lower at early, mid-, and late pregnancy, respectively, in dolphins with stillbirths than in those with live births. In conclusion, the pregnancy-specific increase in serum concentrations of relaxin and lower concentrations of both relaxin and progesterone in association with stillbirths suggest the potential for relaxin to be used diagnostically to determine pregnancy status, and one or both hormones to be used to assess placental function, and, perhaps, fetal well-being in bottlenose dolphins and other cetaceans.