Abstract

Beta MSH is known to lack lipolytic or corticotropic activity in the rat. In intact rabbits, the injection of 10–100 ng purified porcine β-MSH not only elevated serum free fatty acid (FFA) concentration 2 hr later, but also caused a reduction in blood lymphocyte count and a marked increase in serum corticosterone concentration. The effects of 10 and 100 ng (8-MSH on blood lymphocytes, serum FFA and serum corticosterone were similar in magnitude to those produced by 10 and 100 μg oxycellulose- purified ACTH. Lipolytic assays showed the ACTH preparation to be active on rat and hamster adipose tissues at a concentration of 0.01 μg/ml, and the β-MSH preparation to be inactive at 10 μg/ml. In the hypophysectomized rat 0.15 μg of the ACTH preparation depleted adrenal ascorbic acid content, while 500 Mg of the β-MSH preparation had no effect. Therefore, the β-MSH preparation contained less than 0.03% ACTH. These data suggest that β-MSH may possess substantial corticotropic activity in the rabbit. (Endocrinology 86: 1410, 1970)

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