Human pituitary growth hormone. Intrinsic lipolytic activity on rabbit fat cells.

The stimulation of lipolysis in isolated rabbit fat cells by human growth hormone was investigated in detail. The action of the hormone on rabbit adipocytes is very similar to that of adrenocorticotropin and the melanotropins. The effect is rapid, requires Ca²⁺, appears to be mediated by cyclic AMP, and is not blocked by inhibitors of protein synthesis. The lipolytic action of human growth hormone was neutralized by antisera to itself and to human chorionic somatomammotropin. Several lines of evidence indicate that the rapid lipolytic activity of the growth hormone in rabbit fat cells in an intrinsic property of the hormone, although the physiological significance of this activity remains obscure.