PLASMA-CONCENTRATIONS OF IMMUNOREACTIVE RELAXIN ACTIVITY AND PROGESTERONE IN THE PREGNANT ASIAN ELEPHANT (ELEPHAS-MAXIMUS)

Immunoreactive relaxin activity and progesterone concentrations in wee kly plasma samples were measured throughout six pregnancies in five As ian elephants (Elephas maximus). One animal aborted, one delivered a s tillborn calf at term and the remaining pregnancies concluded normally with living young. Immunoreactive relaxin activity increased by week 20 of pregnancy to reach a mean peak concentrations of > 6 ng/ml in th e second trimester. This was followed by a slow decline beginning appr oximately at 30 weeks before term. A smaller, secondary relaxin rise w as observed during the final eight weeks preceding parturition and cir culating concentrations remained above pre-pregnancy baseline values f or 72 h after birth. In contrast, progesterone concentrations increase d immediately after mating and rose to a maximum of > 2 ng/ml by mid-g estation. As with relaxin, progesterone concentrations began to declin e gradually approximately 30 weeks before birth. More frequently colle cted samples before, during and after parturition revealed a decline t o pre-pregnancy levels between 2-5 days before parturition, in contras t to elevated relaxin levels (1 ng/ml) during this time. The aborted p regnancy at week 35 was accompanied by a precipitous decline in both i mmunoreactive relaxin and progesterone concentrations one week before the visible termination of the pregnancy. The delivery of the term sti llborn calf occurred five weeks after both immunoreactive relaxin and progesterone concentrations had declined to pre-pregnancy values. Resu lts suggest that immunoreactive relaxin may be important, along with p rogesterone, in the maintenance of pregnancy in the Asian elephant as well as playing a role in preparation for birth and possibly to indica te foetal well-being. (C) 1998 Elsevier Science B.V. All rights reserv ed.