LAUSR

Abstract Glucocorticoids modulate the feto-maternal interface during the induction of parturition. In the dog, the prepartum rise of cortisol in the maternal circulation appears to be erratic, and information about its contribution to the prepartum luteolytic cascade is scarce. However, the local placental upregulation of glucocorticoid receptor (GR/NR3C1) at term led to the hypothesis that species-specific regulatory mechanisms might apply to the involvement of cortisol in canine parturition. Therefore, here, we assessed the canine uterine/utero-placental spatio-temporal expression of hydroxysteroid 11-beta dehydrogenase 1 (HSD11B1; reduces cortisone to cortisol), and -2 (HSD11B2; oxidizes cortisol to the inactive cortisone). Both enzymes were detectable throughout pregnancy. Their transcriptional levels were elevated following implantation, with a strong increase in HSD11B2 post-implantation (days 18–25 of pregnancy), and in HSD11B1 at mid-gestation (days 35–40) (P < 0.05). Interestingly, when compared pairwise, HSD11B2 transcripts were higher during post-implantation, whereas HSD11B1 dominated during mid-gestation and luteolysis (P < 0.05). A custom-made species-specific antibody generated against HSD11B2 confirmed its decreased expression at prepartum luteolysis. Moreover, in mid-pregnant dogs treated with aglepristone, HSD11B1 was significantly higher than -2 (P < 0.05). HSD11B2 (protein and transcript) was localized mostly in the syncytiotrophoblast, whereas HSD11B1 mRNA was mainly localized in cytotrophoblast cells. Finally, in a functional approach using placental microsomes, a reduced conversion capacity to deactivate cortisol into cortisone was observed during prepartum luteolysis, fitting well with the diminished HSD11B2 levels. In particular, the latter findings support the presence of local increased cortisol availability at term in the dog, contrasting with an enhanced inactivation of cortisol during early pregnancy. Summary Sentence The canine placenta appears to have increased trophoblast-mediated inactivation of cortisol during mid-pregnancy, whereas parturition appears to be marked by increased local cortisol availability. Graphical Abstract