Regional Differences in the Molecular Weight Profiles of Corticotropin and a-Melanotropin in the Hypothalamus*

The molecular weight profiles of immunoreactive ACTH (ACTHi) and immunoreactive α-MSH (α-MSHi) were investigated in two regions of the hypothalamus: the region that is known to contain the perikarya of the ACTH/α-MSH neurons (medial basal hypothalamus) and a region that contains axons of these perikarya (preoptic anterior hypothalamus). Acetic acid extracts of the entire hypothalamus, medial basal hypothalamus, and preoptic anterior hypothalamus obtained from adult male rats were subjected to gel filtration under denaturing conditions. ACTHi and α-MSHi were quantified by RIA. The gel filtration profiles of ACTH in extracts of the entire hypothalamus were indicative of the presence of three molecular weight classes of ACTHi: big ACTH (mol wt, ≥9000), 5.7K ACTH (mol wt, ∼5700), and 4.5K ACTH (mol wt, ∼4500). The molecular weight profiles of ACTHi and the molar ratio of αMSH i to ACTHi in the medial basal hypothalamus and in the preoptic anterior hypothalamus differed markedly. Of the total ACTHi in the medi...