COMPARISON OFIN VITROANDIN VIVOASSAYING PROCEDURES FOR RAT ADENOHYPOPHYSIAL CORTICOTROPHIN1

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Abstract
The same rat pituitary extract was concurrently assayed against the same standard (U.S.P. Reference Standard Corticotropin) by procedures respectively based on in vitro corticoidogenesis, and on in vivo corticoidogenesis and adrenal ascorbic acid depletion. Nearly identical values (20-24 mu. ACTH/mg. fresh tissue) were obtained on the basis of in vivo corticoidogenesis and ascorbic acid depletion, whereas a markedly higher concentration (62 mu./mg.) was recorded on the basis of in vitro corticoidogenesis. These findings do not support Birmingham et al.''s hypothesis of a higher steroidogenic ascorbic acid-depleting activity ratio in rat pituitary extract than in the reference standard. The discrepancy in the results yielded by the two types of procedures appears to be related to differences in the nature (in vivo or in vitro) rather than in the end-points (adrenal ascorbic acid depletion or stimulation or corticoidogenesis) of the assays.