Adrenocorticotropin immunoactivity in monkey hypophyseal portal blood.

ACTH was measured with both C-terminal and midportion antibodies in monkey hypophyseal portal plasma, and compared to levels in monkey peripheral plasma, medial basal hypothalamus, and anterior pituitary. In nine female monkeys, mean hypophyseal portal blood C-terminal ACTH immunoactivity was 5290 +/- 2010 (SEM) pg/ml, whereas the mean midportion ACTH level was 949 +/- 178 pg/ml. These immunoactivities were not lower in two monkeys that were completely hypophysectomized 30 min before portal blood collection. The ratio of C-terminal to midportion ACTH immunoactivity was 4:1 in two monkey medial basal hypothalami, and 1:1 in four monkey anterior pituitary glands. Gel filtration of hypophyseal portal plasma extract and of medial basal hypothalamus showed that the C-terminal ACTH immunoactivity eluted in the same position as the corticotropin-like-intermediate lobe peptide standard. The similarity of the C-terminal to midportion ACTH ratios in monkey medial basal hypothalamus and portal blood, and the observation that ACTH immunoactivity was not significantly lower in two hypophysectomized monkeys suggests that portal blood C-terminal ACTH immunoactivity is of hypothalamic rather than pituitary origin. We conclude that monkey hypophyseal portal blood contains high levels of a C-terminal fragment of ACTH, which coelutes with corticotropin-like intermediate lobe peptide on gel filtration, and which is secreted from the brain directly into the portal circulation.