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)