Adrenomedullin 2 (ADM2) is a recently discovered member of the calcitonin/calcitonin gene-related peptide family with an exon-intron structure similar to that of ADM. The mRNA of ADM2 is expressed in several tissues, including uterus and ovary. The present study was designed to assess the effects of ADM2 antagonist (ADM2_17–47) infusion to pregnant rats on fetal and placental growth. On Day 15 of gestation, rats were implanted s.c. with osmotic minipumps delivering 50 and 200 μg per rat per day of ADM2_17–47 and were killed on Gestational Day 18. In ADM2_17–47-treated rats, placental weights were significantly inhibited in a dose-related manner, with an 11% reduction in the group of rats receiving 200 μg/day, whereas the fetal weights were reduced by 17% without significant differences between the two doses. 2 In ADM2_17–47-infused rats, increased apoptosis was demonstrated in the labyrinth and junctional zones of rat placenta by the TUNEL method compared with the control animals. Western blot analysis demonstrated that in ADM2_17–47-treated rats Bcl-2, mitochondrial cytochrome c, and active caspase-9 and caspase-3 were significantly increased compared with the controls. No significant treatment-associated changes were observed in Bax, Bid, p53, and caspase-8 and caspase-10 proteins in the treated placentas. In addition, infusion of ADM2_17–47 caused a significant decline in the transcripts of nitric oxide synthase 3 (NOS3) and NOS2. These findings show that ADM2_17–47 infusion in rats during midpregnancy cause fetoplacental growth restriction through the activation of mitochondrial apoptotic pathways. This study demonstrates for the first time (to our knowledge) a potential role for ADM2 in placental functions during pregnancy.