The Development of Corticotrophs in the Fetal Sheep Pars Distalis: The Effect of Adrenalectomy or Cortisol Infusion

At 90 days gestation a uniquely fetal-type and an adult-type corticotroph have been observed in the fetal sheep pars distalis (term ∼147 days). Between 90 and 130 days gestation the fetal type is predominant, and its numbers decline toward term. In this study the effect of the endogenous cortisol surge on the change in the population of corticotrophs in the pars distalis was investigated in sheep fetuses after bilateral adrenalectomy at 120 days gestation or after an infusion of 2 mg cortisol/day between 109 and 115 days gestation. The total proportion of corticotrophs, expressed as a percentage, decreased significantly (P < 0.01) from 115 days in salineinfused controls (21.09 ± 1.10%) and 135 days in intact controls (14.59 ± 1.12%). The percentage of adult-type corticotrophs increased significantly (P < 0.01) from 5.65 ± 0.77 at 115 days, to 11.93 ± 1.41 at 135 days. The percentage of fetal-type corticotrophs decreased significantly (P < 0.001) from 14.91 ± 0.35 at 115 days to 2.33 ± 0.48 at 135 days. A ...