In extracts of anterior pituitary tissue obtained at autopsy of fetal, infant, and adult humans, five molecular forms of immunoreactive ACTH (ACTH(i)) were detected that had apparent molecular weights of approximately 40-44, 30-34, 2428, 16-18, and 4.5 kilodaltons (K). The relative proportion of each molecular form of ACTH(i) was similar in tissues that were extracted at the time of autopsy and in tissues that were stored frozen (-20°C) for up to 2 years prior to extraction. We found that 40-44K ACTH(i) comprised a significantly greater proportion of total ACTH(i) in fetuses (12.3 ± 3.5%) than in adults (3.8 ± 0.8%); intermediate amounts of this form of ACTH(i) (8.0 ± 4.1%) were found in tissues obtained from infants. On the other hand, the proportion of 4.5 K ACTH(i) in fetal pituitaries (67 %) was less than that in those of adults (84 %). The ratio of 40-44/30-34K ACTH(i) was significantly greater (P<0.001) in fetuses (1.46 ± 0.12) and infants (1.31 ± 0.07) than in adults (0.52 ± 0.07). The ontogenetic differences in molecular forms of pituitary ACTH(i) are thought to reflect alterations in the processing of proopiomelanocortin as a function of human development.
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