Abstract
In order to determine whether cortisol acts directly at the level of the fetal pituitary to promote pars distalis corticotroph maturation, we have infused cortisol into the hypothalamo-pituitary-disconnected (HPD) fetal sheep from 111 to 117 days of gestation. In this study we have measured fetal plasma cortisol and immunoreactive adrenocorticotrophic hormone (ir-ACTH) concentrations between 105 and 116 days of gestation, and we have determined the proportions of adult- and fetal-type corticotrophs in the pars distalis of catheter control fetuses and in HPD fetuses infused with either saline (HPD+SAL) or cortisol (2 mg/day; HPD+F). The fetal plasma cortisol concentrations did not change significantly following HPD. The mean fetal plasma cortisol concentration between 113 and 116 days was threefold higher in the HPD+F fetuses than that measured in HPD fetuses. Following HPD, fetal plasma ir-ACTH concentrations were significantly higher than in catheter control fetuses. Despite the significant elevation in plasma cortisol concentrations in HPD+F fetuses between 113 and 116 days, plasma ir-ACTH concentrations were not different in these fetuses from HPD fetuses infused with saline. At 117 days of gestation in HPD+F fetuses, the proportion of fetal-type corticotrophs in the pars distalis was significantly less than in the HPD+SAL fetuses; however, there was no significant change in the proportion of adult-type corticotrophs in the pars distalis following cortisol infusion. We have shown that cortisol has a direct trophic effect on the maturation of the pars distalis corticotrophs; however, the full maturation of these cells requires an intact hypothalamo-pituitary axis. These findings demonstrate the importance of the fetal hypothalamus in anterior pituitary corticotroph maturation during the last third of gestation.
Published Version
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