Evaluation of the reflectometric method using the skin of the toad Bufo arenarum in vitro for the determination of plasma MSH

: The aim of the present paper was to investigate the following points, by using the reflectometric bioassay for melanocyte-stimulating hormone (MSH) with skin of the toad Bufo arenarum: (1) To study if solutions of alpha-MSH prepared in rat plasma and amphibian Ringer, or dilutions of plasma overloaded with endogenous MSH, could render in acceptable dose-response lines. 2) To investigate if ACTH at a very high level of plasma concentration could interfere in the bioassay 3) Observing if the storage of plasma could inactivate the inherent MSH activity. 4) Searching for the response of the skins along the 12 months of the year. The results showed that: Acceptable dose-response lines were obtained with the three types of dilutions and parallelism was found among the three lines. ACTH does not interfere in the assay. Almost a total inactivation of MSH was detected after storing the plasma at room temperature for 4 hours; Trasylol or low temperature preserved the hormone activity. Maximal response of the skin corresponded to the minimal concentration of 1 562 pgr/ml, during the whole year. Minimum detectable concentration varied within the range 24-390 pgr/ml, depending on the month when the study was performed.