Postnatal involution of the human adrenal fetal zone: stereologic description and apoptosis

During the first weeks of postnatal development the fetal zone (FZ) of the human adrenal cortex rapidly disappears. Present studies aimed to describe cellular aspects of this involution and to correlate them with apoptosis. Adrenals of 38 newborns and infants (aged 1-240 days) were obtained from autopsies due to accidental death. Postnatal decrease in the adrenal gland weight may be divided into 2 distinct phases: rapid one lasting from the birth till the end of the second week of life, and followed by a slower one. This decrease is highly correlated with the decrease of both: the volume of FZ and quantity of its cells. During the whole investigated period, volume of the FZ decreases from 8,017 to 248 mm3 (from 70 to 3% of total adrenal volume) and the quantity of its parenchymal cells from 3 x 10(9) to 0.15 x 10(9) (from 40 to 5% of all parenchymal cells). The average volume of the FZ cell decreases from 2,200 to 1,400 microm3. The volume of FZ stroma (connective tissue and blood vessels) expands notably during the first day and decreases from day 5th of life. The apoptotic index of the FZ parenchymal cells is the highest during the second week of life (ca 30%), and subsequently declines (ca 20%). Thus, the rapid involution of the FZ is connected with marked hemorrhagic changes and increased apoptotic index of parenchymal cells, while during the slow phase (after 2nd week on) apoptotic index is lower and rather constant.