A biological unit of androgenic activity, which is the masculinizing effect of a substance. Symbol, CU. One CU is the smallest amount of any substance having androgenic activity that, given on two successive days to a capon (a rooster whose testes have been removed), causes its comb to enlarge 20%.
The international unit of androgenic activity was abandoned in 1950. It equaled 0.1 mg of androsterone, which is roughly the activity of 1 capon unit. Androsterone is a steroid metabolite with weak androgenic properties, formed in the testes from progesterone and in the liver by metabolizing testosterone.
K. Diem and C. Lentner, editors.
Documenta Geigy. Scientific Tables. 7th edition.
Ardsley, NY: Geigy Pharmaceuticals, 1970.
U. C. McGee.
Proceedings of the Institute of Medicine of Chicago, vol. 6, page 242 (1927).
The Second Conference on the Standardization of Sex Hormones (Quart. Bull. Hlth. Org. L.o.N., 1935, 4, 618) recommended that “on the information before the conference the test based on the induction of growth in the comb of the capon is, at present, the only one sufficiently specific for the quantitative determination of activity in comparison with the standard preparation.” The conference also agreed that the international standard preparation for male-hormone activity should consist of crystalline androsterone and that “the unit of activity shall be defined as the activity of 0.1 mg: of this standard as tested by a specific biological reaction; this weight is approximately the daily dose required to give an easily measurable response in the comb after five days.” An increase in comb size of about 5 mm. in length plus height or 15 per cent. increase in area may be expected from one international unit (I.U.) daily for five days. Detailed techniques have been described by Dodds et al. (1930), Schoeller and Gehrke (1931), Freud et al. (1932), and Greenwood et al. (1935), as well as by the Chicago workers referred to above.
R. K. Callow and A. S. Parkes.
The chemistry and assay of male hormones.
The British Medical Journal, issue 3973 (Feb 27, 1937).
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