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SUMMARY Attempts to isolate, free of thyroid-stimulating hormone (TSH), the peptide(s) responsible for the lipolytic activity of a fraction of acetone-dried human pituitary powder are described. It was not found possible to separate the lipolytic and TSH activities, even by isoelectric focusing which gave fractions consisting predominantly of single protein components. In the four lipolytic fractions isolated by electrofocusing, the two activities paralleled one another. It is therefore concluded that the TSH present is responsible for the lipolytic activity of this human pituitary fraction, though some evidence suggests that luteinizing hormone (LH), which is a minor contaminant, might also be lipolytic. The minimum effective lipolytic concentration of the most potent fraction isolated was in the range 0·1–1·0 μg/ml. This is far in excess of plasma concentrations of TSH or LH encountered physiologically. Hence the lipolytic action of these molecules is unlikely to be of physiological significance.
Storring et al. (Fri,) studied this question.