RE-INTRODUCTION AND EVALUATION OF AN ACCURATE, HIGH CAPACITY BIOASSAY FOR MELANOCYTE-STIMULATING HORMONE USING THE SKIN OF ANOLIS CAROLINENSIS IN VITRO

Abstract

A simple and rapid assay for the quantitative determination of melanocyte-stimulating hormone (MSH) activity, using skin fragments of the lizard Anolis carolinensis in vitro, is described in detail. This assay, in which a quantal response (e.g. induction of a brownishgreen colour) can be detected by visual observation, allows determination of MSH activity in up to 50 samples/day by one person, using the skin of one lizard. The mean dose found to induce this colour change was 0·15 ng synthetic α-MSH/ml (range 0·02–0·5 ng/ml). The assay shows high accuracy, reproducibility and specificity. Anterior and posterior lobe hormones as well as pituitary catecholamines do not interfere with the determination of pituitary MSH activity. The method is compared with the assay using hypophysectomized frogs (Rana pipiens) in vivo. Determinations of MSH in pituitary extracts by both methods gave quantitatively similar results when determined with α-MSH as the reference substance. However, when β-seryl MSH was used as a reference, the two assays gave different results for the MSH activity of the pituitary extracts. This indicates that MSH from the rat pituitary gland has a biological activity similar to that of α-MSH rather than to that of β-seryl MSH.