MELANOPHORE REACTION AND ADRENO-CORTICOTROPHIC HORMONE

Abstract

A method is descr. for measuring the reflectance of frog melanophores. The reflected light is decreased when melanophores expand. Injn. of intermedin or ACTH causes measurable darkening within 5-10 min., with max. effect at 1-2 hrs. A linear response occurs when the log. dose is plotted against color density, for doses from 0.4-10.0 [mu]g., whether thigh or back was read. Adequate accuracy was obtained with 3 dose levels and 10 frogs to each level. Microscopic estimation of melanophore expansion was accomplished by examination of the web of the foot opposite the injn. side before and 2 hrs. after the test dose. Only frogs with punctate melanophores before injn. were studied. Responses were graded semiquantitatively according to the shape and spread of the melanophores and the reading expressed as the "melanophore index." Results by photoelectric estimation were compared with melanophore index estimations and found comparable. The greater ease of melanophore index detn., and its equivalent accuracy make it preferable to the photoelectric method.