Extrahypophysial distribution of corticotropin as a function of brain size.

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Abstract
Radioimmunoassay determination of corticotropin in brains of rats, rabbits, dogs, [rhesus] monkeys and humans reveals that the dimensions within which the hormone is found are about the same for each of these species, but that the anatomical regions in which the hormone is found depend on brain size. Corticotropin is widely distributed in rat brains but is found only in the hypothalamic region of the primate brain. Patterns of immunoreactivity observed after Sephadex gel filtration confirm that molecular forms of corticotropin found in extrahypophysial regions are similar to those in the pituitary of each species. Apparently the mammalian pituitary is the sole site of synthesis of the hormone. Eight weeks after hypophysectomy the rats from commercial sources apparently manifest stress-stimulated plasma corticotropin concentrations about 80% of that found in intact rats in spite of the fact that residual pituitary tissue was not found by visual inspection of the sella. Scrapings from the sella revealed a corticotropin content up to 5% that of the average rat pituitary.