Demonstration that Cyclic Adenosine 3',5'-Monophosphate Mediates the Lipolytic Action of Parathyroid Hormone

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Abstract
Studies were carried out with rat epididymal fat pads first to compare the effects of the synthetic N-terminal 1-34 peptide of bovine parathyroid hormone and of the native hormone to determine whether this portion of the molecule is responsible for the lipolytic action of the hormone and second to determine whether this biologic action of parathyroid hormone is mediated by cyclic adenosine 3',5'-monophosphate. The N-terminal polypeptide was as effective as the native hormone in stimulating lipolysis in the concentration range between 10-8M and 10-6M. Parathyroid hormone stimulated lipolysis by isolated fat cells. The concentration of cyclic adenosine 3',5'-monophosphate in the fat pads was significantly increased by the hormone (10-6M). Lipolytic stimulation by parathyroid hormone (10-6M) was diminished by insulin (100 µU/ml) and prostaglandin E1 (1 µg/ml), both of which are known inhibitors of lipolysis. The findings indicate that the amino-terminal 1-34 peptide portion of parathyroid hormone is responsible for the lipolytic action and that this effect is mediated through cyclic adenosine 3',5'-monophosphate. 1 The study was supported in part by research funds from the Veterans Administration and by Contract NO 1 AM 4-2223 and Grant AM 15788 from the U.S. Public Health Service.