The winter Necturus hypophysis both whole and selectively divided was extracted in N/10 HCl (0.25 ml per gland or gland portion). Extracts were diluted with normal saline (1:100 and 1:400) and injected 2 ml/100 gm body weight) into groups of 10 or 12 male, hydrocortisone-blocked assay rats (method of Hodges and Vernikos ('60). Groups of control hydrocortisone-blocked male rats received corresponding volumes of a standard ACTH solution. ACTH content of extracts was appraised by measuring the adrenal ascorbic acid depletion induced as compared with control depletions. A 2 + 2 assay design was employed; results and their fiducial limits (P = 0.95) calculated.
The ACTH content of the anterior zone of pars buccalis is that of the entire hypophysis. No ACTH was detected in gland portions consisting of the basophilic bed and transitional zone of pars buccalis plus the neural lobe of pars neuralis. ACTH occurs throughout the anterior zone but is more abundant in its caudal two-thirds both in milliunits (mU) per milliliter of extract and mU/mg of pituitary tissue. This distribution of corticotrophic activity is coincident with the distribution of anterior zone acidophile cells.
Regional and cellular sources of ACTH in mammals and amphibia are discussed.