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ACTH-induced steroidogenesis in isolated rat adrenal cells was markedly increased by commercially available preparations of calcitonin and hCG, but neither synthetic eel calcitonin nor highly purified hCG preparation had the same effect. The ACTH-potentiating activity was present in a variety of normal rat tissues including the cerebrum, the thyroid, the lung and the liver. We recently demonstrated the presence of factors in rat pituitary glands which enhance the steroidogenic response to ACTH of rat isolated adrenal cells in vitro (Iida, et al., 1981). We also noted that these factors exerted a potentiating activity not only on the action of corticotropin-(1-24)-tetracosapeptide [ACTH-(1-24)] but also on the action of (1-glycine)-ACTH-(1-18)-octadecapeptide amide [ACTH-(1-18)]. Furthermore this activity was found, upon gel filtration of the pituitary extracts, in several fractions with molecular weights of 8,000, 12,000 and 15,000. These findings prompted us to investigate whether the activity was included in any known pituitary hormones and whether the factor might be present in other tissues. In this communication, we report the results indicating the presence of ACTH-potentiating activity in hormone preparations as well as in various rat tissue extracts. Materials and Methods The ACTH preparation used was ACTH-(1-18) (Shionogi Pharmaceutical Co., Osaka, Japan). Available pituitary and related hormones tested for ACTHpotentiating activity were: HGH (Kabi, Sweden), prolactin (Daiichi Chemical Isotope Co., Tokyo, Japan), TSH (Sigma), pregnant mare serum gonadotropin (FSH), human chorionic gonadotropin (hCG), highly purified hCG (with a specific activity of 13,000IU/mg), oxytocin (the above four from Teikoku-Zoki Co. Tokyo, Japan), 1-desamino-8-d-arginine-vasopressin (DDAVP) (Ferring Sweden), endorphin (Sigma), porcine calcitonin (Armour Pharmaceutical Co., Ltd.), synthetic eel calcitonin (Toyojozo Co., Shizuoka, Japan) and synthetic vasoactive intestinal peptide (VIP) (donated by Dr. N. Yanaihara, Shizuoka College of Pharmacy, Shizuoka, Japan). For hormones with welldocumented normal plasma levels the concentration was adjusted so that the final level was ten times higher than normal. Various tissues of male Wistar rats, weighing 200g, were removed immediately after decapitation and letting of blood. These tissues were homogenized after Received November 9, 1981 252 IIDA et al. Endocrinol. Japon. April 1982 being boiled for 20minutes in 0.1 N acetic acid. The supernatants were collected after centrifugation at 1,000•~g for 10minutes at 4•Ž and the protein concentrations were determined by Lowry's method (1951). Each extract was diluted with Krebs-Ringer bicarbonate buffer containing glucose (200mg/dl) and 0.5% bovine serum albumin (Schwarz-Mann) to give a final protein concentration of 1ƒÊg/ml. Bioassay procedures, including preparation of isolated adrenal cells by the method described by Sayers et al. (1971) and corticosterone determination by competitive protein binding method of Murphy (1967), were followed as described previously (Iida, et al., 1981) using ACTH-(1-18) as the standard. The mean correlation coefficient of standard curves for ACTH-(1-18) (concentrations from 60 to 650 pM) obtained from 12 experiments was 0.956 (range, 0.9350.983). The mean intra-assay variation for ACTH-(118) (60 pM), which was tested in quintuplicate in the same assay, was 9.18% (range, 7.6-11.9%). Using an antiserum directed toward the 19-24 amino acid sequence of the ACTH molecule, radioimmunoassay was carried out as described previously (Itoh, et al., 1981), in which ACTH-(1-39) was used as the standard. The assayable range of ACTH by the method was from 0.6 to 20ng/ml. The mean correlation coefficient of standard curves for ACTH-(1-39) obtained from 10 experiments was 0.950 (range, 0.9100.977).The mean intra-assay variation was 12.0% (range, 6.18-22.10%). Statistical analysis was done by Student's t-test.

Augmentation of ACTH-induced steroidogenesis in isolated rat adrenal cells by rat tissue extracts and by hormone preparations.