To determine whether the rapid lipolytic effect observed with human growth hormone (hGH) preparations in rabbits and rabbit adipose tissue is an intrinsic property of the hormone, we examined the lipolytic effects in vivo and in vitro of clinical grade preparations, hGH purified by DEAE cellulose chromatography, and hGH prepared by recombinant DNA techniques. Using isolated rabbit perirenal adipocytes, ACTH and clinical-grade hGH preparations both stimulated glycerol release to the same maximal rate with half-maximal hGH effects observed between 8 and 50 micrograms/mL. Purification of the most potent lipolytic preparation of clinical grade hGH by DEAE cellulose chromatography yielded a preparation (2 IU/mg of growth activity that retained insulinlike effects on rat fat pad [U-14C] glucose metabolism) that, at concentrations up to 0.2 mg/mL, failed to stimulate lipolysis by adipocytes incubated for one or four hours in the presence or absence of dexamethasone or trypsin inhibitor or when preincubated for three hours prior to addition of hGH. Recombinant DNA-derived hGH did not stimulate glycerol release at 0.1 mg/mL. While antiserum to purified hGH blocked the increase in glucose oxidation in rat fat pads produced by clinical grade hGH, it did not inhibit its lipolytic effect using rabbit adipocytes. Purified hGH (0.1 mg/kg IV) was also unable to elicit a rise in serum free fatty acid (FFA) levels of conscious rabbits while, at the same dose, clinical grade hGH increased FFA levels to 900 microEq/L over basal. Rapid lipolytic stimulation in rabbit adipocytes by hGH preparations could not be attributed to the 20,000 molecular weight variant of hGH (hGH20K) or the peptide corresponding to positions 32 to 46 of hGH (deletion peptide).(ABSTRACT TRUNCATED AT 250 WORDS)