A radioimmunoassay procedure for quantitating parotid hormone

Cloning and Functional Study of Porcine Parotid Hormone, a Novel Proline-rich Protein

A parotid gland hormone that stimulates intradentinal fluid movement is believed to play a significant role in maintaining the vitality of dentin. This hormone has been purified from porcine parotid glands and partially sequenced in our previous study (Tieche, J. M., Leonora, J., and Steinman, R. R. (1980) Endocrinology 106, 1994-2005). We now report the cloning and functional study of porcine cDNAs that code for this hormone and its complete amino acid sequence. Three cDNA clones were isolated from a porcine parotid cDNA library. The last 30 amino acids encoded by two of the cDNAs agreed with the amino acid sequence of the isolated parotid hormone. In situ hybridization and immunohistochemical staining demonstrated that the acinar cells of the parotid glands were the primary location for both the parotid hormone-related mRNAs and the translation products. A 216-bp fragment of the cDNA that contains the coding sequence for the porcine hormone was subcloned into an expression vector, and the protein expression was detected by immunoblot analysis and quantified by enzyme-linked immunosorbent assay. In addition, the 30-amino acid parotid hormone was synthesized. Both the expressed and the synthetic proteins were biologically active in that they enhanced intradentinal fluid movement as measured by intradentinal dye penetration.

Biological and chemical evidence for the existence of a porcine hypothalamic parotid hormone-releasing factor

Methodology has been developed to achieve partial purification of a parotid hormone-releasing peptide from porcine hypothalamus-thalamus tissue using an in vivo parotid hormone stimulation test in pigs and a dentinal fluid transport stimulation test in rats. The purification steps include: acetone-water extraction of the tissue at pH 5.2, ultrafiltration through Amicon PM10 membrane, size exclusion chromatography on Bio-Gel P2, and open-column reversed-phase chromatography on Lichroprep RP8. A 100-fold increase in specific activity was attained. Intravenous infusion of porcine hypothalamus-thalamus extract stimulates a dentinal fluid transport mechanism in teeth of intact anesthetized rats, and the release of plasma immunoreactive parotid hormone in conscious catheterized pigs. Parotidectomy in both species suppresses the response, suggesting that the expression of parotid hormone-releasing activity requires the integrity of a putative hypothalamus-parotid gland endocrine axis.

Physiological factors affecting secretion of parotid hormone

A parotid hormone (PH) that stimulates a dentinal fluid transport (DFT) mechanism in rat teeth is part of the hypothalamic parotid gland endocrine axis (HPEA). Infusion of a porcine hypothalamus-thalamic tissue extract (PHTE) into anesthetized rats stimulates the DFT mechanism in intact animals but is ineffective in parotidectomized rats. Infusion of PHTE into intact conscious pigs raises the plasma titer of immunoreactive PH (iPH) five- to eightfold. Parotidectomy prevents the response. The feeding of pig chow is a potent stimulus for iPH secretion: an 11-fold increase is reached within 10-20 min, and the response is directly related to the length of the feeding stimulus. No response is obtained after parotidectomy. The secretion of saliva and iPH from the parotids occurs independently of each other, suggesting different control mechanisms for each function. The immediate secretion of iPH in response to feeding and its relationship to DFT stimulation may represent a systemic physiological process by which resistance of teeth to decay is enhanced at a time when the acidogenic potential of the oral microbes is maximum.