Development of the Porcine Fetal Adrenal in Late Gestation1

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Abstract
Porcine fetal adrenal development at days 89, 97, 105 and 113 of gestation was investigated. Cortisol secretion by fetal adrenal slices in vitro paralleled fetal plasma cortisol levels previously reported by other investigators, with the greatest increase in both occurring during the last week of gestation. Neither the ACTH dose-response nor the proportional increase in cortisol secretion in response to a maximal dose of ACTH changed from day 89 to term. At all ages examined, homologous fetal pituitary homogenate had the same effect on cortisol production as a maximal dose of ACTH. Adrenal cortex ultrastructure appeared well developed from day 89 on. Adrenal weight increased faster than fetal weight, especially between days 105 and 113. This increase was primarily due to hyperplasia in the adrenal cortex zona fasciculata, although some hypertrophy also occurred. The increase in cortisol secretion in vitro between days 89 and 105 could be completely accounted for by adrenal cortex growth. From days 89 to 105, the cortisol:corticosterone ratio as determined by high pressure liquid chromatography (HPLC) was 1.1 .+-. 0.3, but increased (P > 0.05) to 4.8 .+-. 0.5 by day 113. The major adrenal changes contributing to increased cortisol production are mitotic activity in the zona fasciculata which increases as term approaches and increased secretion of cortisol in proportion to other steroids in the last week of gestation.