The effects on rat fat cells and adipose tissue of a bovine adenohypophysial anti-insulin peptide (AIP) were compared to those of various bovine growth hormone preparations. The lipolytic activity of AIP was about 1-2% that of growth hormone on a weight basis. The increase in lipolysis seen with AIP was blocked by cycloheximide. AIP did not alter basal glucose oxidation in fat cells but slightly increased basal glucose oxidation in adipose tissue. AIP also did not inhibit the insulin stimulation of glucose oxidation in free fat cells or adipose tissue. Growth hormone inhibited the increase in glucose oxidation due to insulin but this effect was dependent on lipolysis. Dexamethasone markedly inhibited insulin-stimulated glucose oxidation despite its failure to activate lipolysis. In the presence of dexamethasone the increase in lipolysis due to growth hormone was enhanced. The lipolytic activity of highly purified bovine growth hormone preparations was greater than that of the NIH preparation. The fragment of bovine growth hormone corresponding to residues 96133 had about 3% of the lipolytic activity of growth hormone. It was concluded that AIP did not possess any significant anti-insulin activity on fat cells or adipose tissue but did have a weak lipolytic activity.
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