High-sucrose diet inhibits basal secretion of intradentinal dye penetration-stimulating parotid hormone in pigs.

Earlier studies indicated that feeding rats a high-sucrose diet for 1 wk decreases the intrinsic rate of intradentinal dye penetration in molar teeth. Because intradentinal dye penetration appears to be controlled by a parotid hormone, we investigated the chronic effect of a high-sucrose diet on basal parotid hormone secretion in pigs. In fasted pigs, the plasma immunoreactive parotid hormone titer decreased significantly after substitution of a high-sucrose diet for standard chow and remained at a level 72% lower for 40 days until the diet was reverted to standard chow. Within 3 days of diet reversion, the basal hormone titer returned to its original value. The results indicate that a high-sucrose diet can significantly alter the basal secretion of parotid hormone. The possibility exists that inhibition of intradentinal dye penetration after ingestion of a high-sucrose diet could be the result of depressed parotid hormone secretion.

Further evidence for a hypothalamus-parotid gland endocrine axis in the rat.

The existence of a hypothalamus-parotid gland endocrine axis that stimulates intradentinal dye penetration (IDDP) in rat teeth was suggested in earlier studies and IDDP-stimulating factors were isolated or purified from porcine parotid glands and hypothalamic tissues, respectively. In the present study, infusion of carbamyl-DL-aspartic acid (CAA) into rats was used to demonstrate the role of the endogenous hormones of the hypothalamus-parotid gland endocrine axis in stimulating IDDP, as observed by fluorescence microscopy of longitudinal sections of molar teeth. Intra-arterial infusion of CAA into intact rats stimulated IDDP in a dose-related fashion (between 49-390 nmol/100 g body weight); however, infusion of 390 nmol into parotidectomized rats was ineffective. Infusion of plasma from CAA-treated rats was equally effective in stimulating IDDP in intact and in parotidectomized animals. In contrast, plasma obtained from parotidectomized, CAA-treated rats stimulated IDDP in intact recipient animals but not in parotidectomized ones. Moreover, plasma from adult rats treated with CAA after an electrolytic lesion of the hypothalamus, and infused back into young intact rats, was ineffective in stimulating IDDP. These results indicate that: (1) CAA requires the functional integrity of the parotid gland to express its IDDP-stimulating activity, (2) a hormonal factor is secreted by the parotids in response to CAA stimulation and is directly responsible for IDDP stimulation, (3) release of the endocrine parotid IDDP-stimulating factor after infusion of CAA involves a second endocrine factor that appears to originate from the hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of intradentinal dye penetration by feeding in the rat.

Dentinal fluid movement, as measured by intradentinal dye penetration (IDDP), may be under the control of an endocrine system that includes the parotid glands. It was earlier demonstrated that parotid hormone stimulates IDDP when infused into rats, and in the pig the onset of feeding signals the release into the circulation of immunoreactive parotid hormone (iPH), the titre of which remains elevated for more than 1 h after feeding. As, for technical reasons, it is impossible to measure iPH and IDDP activity in the same animal, the hypothesis that feeding causes IDDP stimulation in the rat was now tested. Feeding rats for 15 min stimulated IDDP to a level significantly higher than when fasting (0.418 +/- 0.040 versus 0.106 +/- 0.022, p < 0.001). Within the experimental conditions, IDDP stimulation lasted longer than 15 min. Sialoadenectomy before the feeding experiment did not change the feeding-stimulated IDDP response unless the parotid glands were removed. In parotidectomized and totally sialoadenectomized rats fed for 15 min, the level of IDDP was not different from that of sham-operated fasting animals. It is postulated that, in addition to the existence of possible local regulatory factors in the pulp, dentinal permeation may be under a physiological control mechanism involving a parotid endocrine function. It is also suggested that a hormonally controlled mechanism of dentinal fluid movement may play a systemic, protective role against the bacterial acidogenic challenge to teeth.

The effect of dietary factors on intradentinal dye penetration in the rat.

Fluorescent dye injected systemically into rats penetrated the dentinal tubules of molar teeth in a dynamic fashion. The presence of dye was established using histological and fluorescence microscopy techniques. The rate of intradentinal dye penetration was dependent on dietary factors: it was high in rats chronically fed Purina rat chow and low in rats fed a cariogenic, high-sucrose diet. In addition, parotidectomized rats showed low levels of intradentinal dye penetration, even though they were maintained on Purina chow. One and 2 ml of plasma from Purina-fed rats were effective in stimulating the dye penetration in intact and parotidectomized rats, whereas 2 and 4 ml of plasma from rats fed a high-sucrose diet were ineffective when infused in either intact or parotidectomized animals. The results suggest that rats fed Purina chow have a significantly higher titre of a circulating, dye penetration stimulating factor than animals fed a high sucrose diet. This circulating factor could be the equivalent of the parotid hormone isolated from porcine tissue. It is suggested that dietary factors may affect secretion of a parotid hormone and thereby regulate the rate of dentinal fluid movement. There is therefore the prospect of a functional relationship between diet, the regulation of dentinal fluid flow by an endocrine system and dental health.

Isolation and partial characterization of a porcine parotid hormone that stimulates dentinal fluid transport.

A parotid hormone (PH-A beta) has been isolated and purified from porcine parotid glands. The biological effect of the hormone is the stimulation of a dentinal fluid transport (DFT) in molar teeth of rats. The method for purifying the PH-A beta includes: extraction at pH 7 and 5, ultrafiltration through Amicon membranes, ion exchange chromatography on carboxymethyl cellulose, gel filtration on Sephadex G-50, and preparative electrophoresis in polyacrylamide gel. The PH-A beta is characterized as a glycoprotein having a molecular weight of 8100 and containing 2% hexose. The amino acid composition suggests a molecule rich in glycine (46%) and proline (27.7%). Alanine, glutamic acid, arginine, serine, aspartic acid, leucine, and lysine account for the remaining 26% of the residues. The isoelectric point is pH 7.50. The partial N-terminal amino acid sequence was determined to be: NH2-Ala-Pro-Pro-Gly-Ala-Arg-Pro-Pro-Pro-Gly-Pro-Pro-Pro-Pro-Pro-Pro-(Glu)-(Pro)-?-(Pro)-(Pro)-Arg-(Pro)-(Pro)-(Pro)-Gly-(Gly)-(Gly). A 5.5 X 10(7)-fold increase in DFT activity has been achieved relative to the crude gland extract. As little as 9.7 pg PH-A beta are effective in stimulating DFT. The significance of the PH-A beta appears to be the maintenance of a functional DFT within teeth to allow the avascular dental tissues to meet their high metabolic requirements.

The effect of desalivation upon pulpal function and dental caries in rats.

The role of pulp and saliva in caries susceptibility and resistance was evaluated using a combination of endodontic treatment and desalivation. Evidence was presented that the pulp plays a major role in caries susceptibility. It is suggested that pulpal function is modified by hormonal factor(s) originating from salivary glands. In the rat, saliva appears to play a minor role in resistance to caries.

Susceptibility to dental caries.

The role of the pulp and saliva in caries susceptibility and resistance was evaluated by a combination of endodontic treatment and desalivation. Evidence was presented that the pulp plays a major role in caries susceptibility. Pulpal activity is modified by a hormonal factor or factors of salivary gland origin. Saliva appears to play a minor role in resistance to caries.

Effect of selected dietary additives on the incidence of dental caries in the rat.

Weanling rats fed a cariogenic diet supplemented with carbamyl phosphate, in combination with egg shell meal and trace elements, showed a striking reduction in the incidence of caries. The cariostatic efficacy of carbamyl phosphate is significant because it stimulates fluid movement within odontoblasts via the hypothalamic-parotid gland endocrine axis.

Acidogenic potential of cariogenic and noncariogenic diets in the rat.

No significant difference in lactic acid content was observed in dood residues removed from the occlusal grooves of rats receiving Purina lab chow or the 62% sucrose cariogenic diet. The incubation of rat saliva with Purina chow, with 62% sucrose diet, or with the 62% sucrose diet supplemented with carbamyl phosphate, egg shell meal, and the trace elements zinc, molybdenum, and chromium produced in 24 hours essentially the same pH surve. The terminaltitratable acidity observed in saliva incubated with the 62% unsupplemented diet, however, was significantly less than that produced in salivary mixtures containing either Purina chow or supplemented sucrose diets.